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THE LIBRARY OF WORK AND PLAY


  CARPENTRY AND WOODWORK
    By Edwin W. Foster

  ELECTRICITY AND ITS EVERYDAY USES
    By John F. Woodhull, Ph.D.

  GARDENING AND FARMING
    By Ellen Eddy Shaw

  HOME DECORATION
    By Charles Franklin Warner, Sc.D.

  HOUSEKEEPING
    By Elizabeth Hale Gilman

  MECHANICS, INDOORS AND OUT
    By Fred T. Hodgson

  NEEDLECRAFT
    By Effie Archer Archer

  OUTDOOR SPORTS, AND GAMES
    By Claude H. Miller, Ph.B.

  OUTDOOR WORK
    By Mary Rogers Miller

  WORKING IN METALS
    By Charles Conrad Sleffel.

[Illustration: Drawing by J. Hodson Redman. Harold Sending the C. Q. D.
Message (_See page 355_).]




                    _The Library of Work and Play_

                          ELECTRICITY AND ITS
                             EVERYDAY USES

                      BY JOHN F. WOODHULL, PH.D.

                            [Illustration]

                          McGOWEN-MAIER & CO.
                             CHICAGO, ILL.




          ALL RIGHTS RESERVED, INCLUDING THAT OF TRANSLATION
          INTO FOREIGN LANGUAGES, INCLUDING THE SCANDINAVIAN

             COPYRIGHT, 1911, BY DOUBLEDAY, PAGE & COMPANY




PREFACE


Why do we pursue one method when instructing an individual boy out of
school, and a very different method when teaching a class of boys in
school?

The school method of teaching the dynamo is to begin with the bar
magnet and, through a series of thirty or forty lessons on fundamental
principles, lead up to the dynamo, which is then presented, with
considerable attention to detail, as a composite application of
principles. This might be styled the synthetic method. He who teaches
a boy out of school is pretty likely to reverse this order and pursue
the analytic method. The class in school has very little influence in
determining the order of procedure. The lone pupil with his questions
almost wholly determines the order of procedure. Out of school no
one has the courage to deny information to a hungry boy; in school
we profess to put a ban upon information giving, and we do quite
effectually deaden his sense of hunger. The school method rarely yields
fruit which lasts beyond the examination period; on the other hand, a
considerable number of boys have become electrical experts without the
aid of a school. This book is the story of how my boy and I studied
_electricity_ together. We have had no other method than to attack our
problems directly, and _principles_ have come in only when they were
needed.

My boy had learned to read when very young by having stories read to
him while he watched the printed pages. The construction of sentences
out of words and words out of letters had come to him very incidentally
but all in due time, and when he first went to school rather late in
life for a beginner he found himself more proficient than the other
boys of his own age both in reading and in understanding the printed
pages. I could see no good reason why he should not pursue the same
method in studying electricity.

We live in a modern apartment house in a great city. My boy likes to
visit engine rooms and talk with the engineers about their machinery.
His mother and I always encourage him to talk with us about the things
in which he is most interested. If the family is alone at dinner, he is
quite likely to lead the conversation into the field of electricity.
When particularly burdened with my work I have learned to find relief
by giving an afternoon to Harold, who generally takes me to some
electrical store or power station or to ride by electric train out into
the country.




CONTENTS


  CHAPTER                                                   PAGE

      I. The Dynamo and The Power Station                      3

     II. Dynamo continued--The Magnet                         11

    III. The Ammeter                                          25

     IV. The Wattmeter                                        35

      V. The Electric Motor                                   43

     VI. Applications of the Electro-magnet                   57

    VII. Electric Heating                                     97

   VIII. Applications of Electric Heating                    107

     IX. Lighting a Summer Camp by Electricity               160

      X. How Electricity Feels                               168

     XI. The Electric Sparking Equipment for a Gasolene
           Engine                                            178

    XII. Electricity From Central Stations                   204

   XIII. Electricity From an Old Mill                        218

    XIV. Doing Chores by Electricity                         240

     XV. Electric currents from Chemical Action and Chemical
           Action from Electric Currents                     248

    XVI. Electrocution at Millville                          271

   XVII. The Telephone                                       274

  XVIII. Electric Bell Outfit for the Cottage                296

    XIX. Using Electricity to Aid the Memory                 300

     XX. The Electric Brick Oven                             305

    XXI. Electric Waves                                      309

   XXII. Ringing Bells and Lighting Lamps by Electric
           Waves                                             324

  XXIII. Telegraphing by Electric Waves                      329

   XXIV. Halley's Comet and Electric Waves                   333

    XXV. How the Idea of a Universal Ether Developed         339

   XXVI. Electric Currents Cannot Be Confined to Wires       349

  XXVII. Wireless Telegraphy In Earnest                      355




ILLUSTRATIONS


  Harold Sending the C. Q. D. Message             _Frontispiece_

                                                     FACING PAGE

  Testing a Generator                                          8

  Wiring                                                      16

  Wattmeter                                                   40

  Testing the Telegraphy Outfit                               62

  Electric Bell                                               72

  Feeling Electricity                                        174

  Operating the Switchboard                                  204

  Induction Coil of a Wireless                               330




ELECTRICITY AND ITS EVERYDAY USES




I

THE DYNAMO AND THE POWER STATION


One day Harold expressed a desire to see the dynamos, five miles away,
which furnish the electric light in our apartment. So I told him to
invite his best friend to accompany us and we would go.

When we were some distance from the station the boys noticed the very
tall chimneys and inquired why tall chimneys were needed for dynamos. I
explained that the dynamos were run by steam-engines, and steam-engines
required the burning of coal. "Oh!" said Ernest, Harold's friend, "I
read in the paper that electricity is the rival of steam and is going
to drive out the steam-engine." I suggested that we were about to see
some steam-engines driving electricity out of that power station. But
more seriously, I explained that steam-engines were used for many
years as locomotives to draw the trains on the elevated railroads of
New York City, and when at last they were displaced by electric trains
some people thought that it was a case of electricity driving out
steam, whereas what had really happened was that the steam power for
running those trains had been concentrated at a central station, and
its power was merely transmitted to the trains by means of electricity.
The trains were, therefore, run by steam power quite as much as ever.
In like manner, the surface cars of New York a few years ago were run
by a cable, which was merely a very long belt used to transmit to the
cars the power of steam-engines located at a central station. When they
were changed to electric cars, electricity became the successful rival
of nothing else than a twisted wire cable. The cars still run by steam
power as before, but that power is transmitted by electricity instead
of the discarded cable. Steam has driven out the horse as a power for
drawing street cars, and electricity has enabled us to gather all the
steam engines into central stations, where now they are furnishing the
power for moving surface, elevated, and subway cars for street traffic,
as also trains for suburban travel. Central station steam-engines
are producing a vast amount of power, distributed all over the city
by means of electricity, for doing a great variety of work and for
furnishing electric light and heat, all of which we shall presently
study. "Just before we go into this central station, can you tell me
how the elevator is run in our apartment house?" "It is an electric
elevator," said Harold. "And where does the electricity come from?" I
inquired. "Well, I know that it comes from the street mains, but do
they come from this power station?" "Yes," said I, "and we will now go
in and see the steam-engines which lift you up stairs many times each
day by sending electricity to run that elevator. If you choose to do
so, you may claim for purposes of discussion that your elevator is run
by steam."

As we entered the building we came first to the dynamo room and both
boys noticed that the tone which met their ears was that which I had
produced for them in the telephone the night before. "I shall try to
show you before we get through," I said, "that these dynamos are doing
something which makes iron pulsate sixty times a second and that that
is the cause of the pitch of this tone. But let us begin with the coal
which is the source of all this power.

"This particular station at the present time is burning forty tons of
coal an hour. That is as much as Mr. ---- uses to heat his twelve-room
house for a whole year. One pound of coal is capable of liberating
enough energy to supply 5-3/4 horse-power for an hour. (Written for
short 5-3/4 H.P.H.) One ton of coal is capable of furnishing (2,000 ×
5-3/4) 11,500 H.P.H. Forty tons would yield 460,000 H.P.H. But the best
furnaces, boilers, and steam-engines are terribly wasteful of energy.
About nine tenths of all this energy is wasted and only one tenth, or
about 46,000 horse-power per hour, is delivered by the steam-engines to
the dynamos.

"Coal is already scarce in the world and the supply is rapidly being
exhausted. Meanwhile we are growing more dependent upon coal. A century
ago we used scarcely any power except that of men, horses, and oxen,
and what little heat men then used came chiefly from wood. They lived
in cold houses, attended cold churches and schools, did not ride in
steam or electric cars, and did not have power plants. Our wood is
nearly all gone, our coal is going, and we are very rapidly growing
more dependent upon heat and power, our chief source of which is coal.
Wind power is too uncertain to depend upon, and we turned our backs
upon water-power when we began to crowd into cities. What little
water-power there is, however, is nearly all in use.

"There is great need both that we learn how to save the major part
of the energy of the coal which we now waste, and that we find a
substitute for the coal to use when that is gone.

"A part of the heat from the forty tons of coal which is being burned
in this particular power plant goes into the water in the boilers. It
converts this water into steam. The steam, if free to expand into the
air, would occupy about one thousand seven hundred times the volume
of the water. We compel it to expand through the cylinders of the
steam-engine, using its force of expansion to make wheels go around--to
make the dynamo revolve. These dynamos are not _devices for producing
power but merely for transmitting_ the power of these steam-engines
to far away places where it may be used, as, for instance, in our
apartment house, where we are unwilling to walk upstairs and want some
power to carry us.

"Our own apartment is fifty feet above the street. I weigh one hundred
and sixty-five pounds. If I walk up stairs from the street to our
apartment in one minute, which is the rate of a rather slow elevator,
I work at the rate of one quarter of a horse-power. One hundred and
sixty-five pounds raised two hundred feet in one minute requires one
horse-power. You boys each weigh about half as much as I do, and if one
of you walks up the same stairs in one minute you exert half the power
that I do, or if you run up the stairs in half a minute you exert the
same power, that is, one quarter of a horse-power. When we three walk
up together in one minute we exert one half horse-power. If we all
three run up the stairs in half a minute we expend one horse-power.
Now, the speed of elevators for apartment houses is about one hundred
feet a minute. We are unwilling to walk up stairs, not because we are
lazy but because we have the New York haste, and so we employ elevators
which run at the rate of about one hundred feet a minute.

[Illustration: Photograph by Helen W. Cooke. Testing a Generator]

"These dynamos enable us to employ the power of this central station
to run the elevator in our apartment house. Here is a dynamo rolling
over now in the act of sending out power, some of which goes to that
elevator; and standing beside it is another waiting to be used when
necessary. Examining these dynamos, we find that they are composed
of nothing else than iron and copper. About all that we can say of
these mysterious machines is that the moving iron generates the
electricity and the copper leads it away.

[Illustration: Fig. 1]

"Each one of these dynamos has many hundred tons of iron in it. A
huge wheel of iron, thirty-two feet in diameter, one hundred feet in
circumference, portions of which are surrounded by insulated copper
conductors, forms the centre-piece of the machine. This movable part
weighs four hundred tons. Around about this is a fixed ring of iron,
portions of which are surrounded by insulated copper conductors.
Ordinarily the ring which is stationary is called 'the field,' and the
wheel, which rotates, is called 'the armature,' although these terms
are sometimes reversed for certain reasons. The movable part in these
machines rotates about once a second, that is, its circumference moves
a little faster than a mile a minute. The iron moving at this high rate
of speed creates ether streams or electric currents, which are led off
by the copper conductors. The generation of electricity on a large
scale requires large masses of iron and high velocity."

I noticed that the boys stood before this machine in a state of
utter bewilderment, bewildered as a man who is told that what he had
considered north is really south, bewildered as a man who, having
wandered through a maze of city streets, looks up at length and
unexpectedly finds the building he has been seeking towering before
him. The questions they asked were entirely without thought. "What is
inside of it?" "Simply more iron and copper, such as you see on the
surface," I replied. "But what makes it go?" "The steam engines, of
course, four of which you see, are coupled directly to each dynamo."
"But where does it get its electricity?" "Don't forget that you are
looking at _a generator_ of electricity. Big mass of iron--rapid
motion! That is the whole truth. But it cannot satisfy you as an answer
until you have become used to it. We have seen all that we ought to
see here to-day. Let us drop the whole matter now, but return to my
laboratory to-morrow, and I will give you the next step which will help
you."

The boys did no talking upon their return journey. Whether one may say
they were thinking or not I cannot tell, but certainly their ideas were
incubating.




II

THE DYNAMO, CONTINUED--THE MAGNET


When we had gathered at my laboratory the next day I took down a spool
of one pound No. 24 cotton-covered copper wire (Fig. 2 _A_), which had
its centre filled with wire nails. The boys had seen it before and
remembered it. With flexible wires I connected the two ends of the wire
on this spool to a sensitive ammeter, _B_, which had its zero in the
middle of the scale, and I laid down upon the table a bar magnet, _C_.

[Illustration: Fig. 2]

"Here," I said, "is a dynamo complete." The bar magnet furnishes the
'field' and this spool of copper wire, _A_, which I will move back and
forth immediately over the magnet from end to end, is 'the armature.'
_D_ and _e_ are the line wires and the circuit is completed through
the ammeter to show whether we are generating electricity. And now as
I move this armature along the field you see the needle of the ammeter
move to the right from zero to ten. When the armature is moved in the
opposite direction along the field the needle moves in the opposite
direction past zero and on to ten at the left. The moving of the needle
in the ammeter shows that we are generating electricity. The swinging
to and fro of the needle shows that we are generating an alternating
current of electricity. It is a mere matter of detail whether we move
the armature or the field, as I will show you by letting the spool A
rest quietly upon the table and moving the magnet to and fro lengthwise
across the end of the spool. Or I may accomplish the same results by
moving them both in opposite directions. It is simply necessary that
they move _with reference to each other_. Some dynamos are made with
stationary fields and rotating armatures, some with stationary armature
and rotating fields, and some with both parts designed to rotate in
opposite directions.

"Magnetism is not confined to the magnet. It extends more or less
widely into the region about it. It is this region affected by the
magnet that we designate its magnetic field. By bringing this sensitive
compass needle into the region of this bar magnet from all directions,
I show you that it has a slight power to change the direction of the
needle when about a foot away. This power grows rapidly greater as the
distance grows less. Of course its field extends rather indefinitely,
but we may say that this particular magnet has an appreciable field
extending about one foot in all directions from it. We find upon
examination that some magnets have bigger and stronger fields than
others, that all have their strongest fields when first magnetized
and lose their strength gradually, _but never entirely_. We find that
hardened iron and steel hold magnetism longer than soft iron, _but
all iron is magnetized somewhat at all times_. Iron that is feebly
magnetized can be made into a strong magnet by bringing it into a
strong magnetic field. The earth is a feeble magnet, and that is why
it gives direction to the compass needle. That is also probably the
reason why every piece of iron upon the earth is a magnet, or, to put
the cause back another step, we may say that whatever causes the earth
to be a magnet also causes every piece of iron upon the earth to be
likewise a magnet.

"But thanks to Oersted in Denmark in 1819 and Faraday in England in
1821 and Joseph Henry in Albany, N. Y., in 1827, we have learned to
make exceedingly powerful magnets by sending a current of electricity
in a whirl around the iron. This is the meaning of the coils of copper
wire around iron cores in the dynamo, in electric bells, in telegraph
sounders, in motors, etc., etc. To prevent the electric current from
taking the shortest route, through the iron core or through the
successive layers of copper wire, the iron core and the wire must
be covered with something like wood or paper or cotton or silk or
rubber--such things as electricity does not readily pass through--that
is, insulating material.

"Joseph Henry, while teaching in the Albany Academy, was the first to
make electro-magnets. There was no such thing as wire covered with an
insulating material then in the market, and he wound all his wire
with silk ribbon. But in the year 1834 he made magnets which lifted
thirty-five hundred pounds, to the astonishment of every one. A pair of
such electro-magnets as I have here (Fig. 3), each consisting of one
pound of No. 24 cotton covered copper wire, eight hundred feet long,
wound in one thousand turns about an iron core two inches in diameter,
will lift several hundred pounds: much more than we three can lift, as
I shall now show you."

[Illustration: Fig. 3]

The cores of the two magnets were bolted fast to an iron beam, and a
large bar of iron with a ring in it was laid across the other free ends
of the magnet cores. I made connections with the electric lighting
circuit (that in my laboratory is what is called a direct current),
and sent a current of electricity around the coils. The two boys and
I tugged at the ring in the iron bar to no avail. We were unable to
pull the iron bar away from the magnet. But when I opened the switch
and cut off the electric current, one boy with one finger in the ring
lifted the bar with perfect ease.

"Electro-magnets are now made with a magnetic intensity 90,700
times that of the earth's magnetism. Electro-magnets are used for
hoisting iron castings weighing many tons. Here is a picture of an
electro-magnet lifting a whole wagon load of kegs of nails from the
wagon to the hold of a ship.

"Electro-magnets are our only means of utilizing electricity for
power. It is the pull of electro-magnets that moves the electric car.
Electro-magnets are now used for pulling all the trains out of the
Grand Central Depot in New York City.

"Let us now compare the strength of our electro-magnet with that of the
bar magnet used in our former experiment."

I opened and closed the switch, which sent the electric current through
my magnet coils at frequent intervals, and the two boys, each with a
compass needle, searched the field for magnetic effects. They found
that the magnetic field extended six or eight feet, but this piece of
research was broken up by a new idea which appeared to strike them both
at the same instant, for they shouted both together, "Let's use this
electro-magnet in place of the bar magnet for our dynamo experiment!"

[Illustration: Photograph by Helen W. Cooke. Wiring]

"That is surely the next step in our programme," said I, "but you will
need a steam-engine to move an armature in this magnetic field, will
you not, judging from the struggle we had with that iron bar a few
minutes ago?" The boys looked quite hopeless until I said, "The best
thing about the electro-magnet remains yet to be told. You have perfect
control of its strength by changing the amount of electricity which you
send around the coil.

"By means of an instrument which works like the motorman's controller
on the electric car, I may control the amount of electricity which
flows, just as well as you may control the flow of water by a faucet or
stop-cock. By this means I will control the strength of the magnet so
that you may move the armature in your dynamo experiment.

"In 1821, Faraday, at the Royal Institution, London, learned that he
could produce magnetism by means of the electric current, and, in
1831, he learned that the reverse was also true, namely, that he could
produce electricity from magnetism. This idea coming as the result of
ten years of incessant search made him shout and dance like a child.
You are feeling a little of the pleasure of his discovery."

[Illustration: Fig. 4]

I then fastened one of the coils upon the table underneath a small
bench (Fig. 4) and sent an electric current around it. The other coil,
_B_, connected with the ammeter was pushed back and forth along the
surface of the bench over this coil. The boys found that the more
electric current I sent around the coil _A_, that is, the stronger I
made the magnetic field, the harder it was to move the coil _B_. They
found that the nearer _B_ was to _A_ the harder it was to move it. They
found that the faster they moved _B_ the more electricity was produced.
They tried laying _B_ upon its side upon the bench and thus moving
it. They tried taking _B_ off the bench and moving it on all sides of
_A_. They found it much harder to move in some ways than in others,
but in all cases they found that the harder they had to work the more
electricity was developed, as was shown by the ammeter.

"The dynamo is any machine which will convert mechanical work into
electricity. The magneto is one form of a dynamo which you have used
much at the summer cottage, but have never seen the inside of. Here are
several (see Figs. 5, 6, and 8) which I will let you examine inside and
out, and with these I must leave you to yourselves for a time."

When I returned I asked the boys why these dynamos were called
_magnetos_. "Because they have steel magnets for their fields," they
replied. "There are several magnets bent in the shape of a horseshoe."

"Yes," I said, "in this case the field is made stronger by taking
several magnets. Have you noticed any armature?" "Yes, it is made of
iron with insulated copper wire wound around it."

"Please recall that the amount of energy you expend in going upstairs
depends on two things: (1) your weight and (2) the speed with which you
move. Also recall that the amount of electricity you could generate
with a dynamo depended upon the amount of energy you expended.
Therefore, the strength of the electric current which this machine
may produce depends upon two things: (1) the strength of the magnetic
field against which you must pull and (2) the speed of the motion of
the armature. Evidently this field is made as strong as it is possible
to make it with steel magnets. Now is there any device for giving high
speed to the armature?"

"Yes, indeed," said the boys, "one has a pulley so that it may be
connected by a belt with a gas engine, and the others have each a large
cog-wheel working into a smaller one. We found in one of them that a
single revolution of the crank gave six revolutions to the armature."

I found that the boys had made large-sized drawings of the parts, and
were preparing to report on the magneto as a form of dynamo at the next
meeting of the Science Club, which we had started among the boys in
school.

[Illustration: Fig. 5]

"I will loan you some apparatus so that you may give a very interesting
demonstration on that subject," said I, "only let me show you how to
use it first. Connect the binding posts _D_ and _E_ of this magneto
(Fig. 5) with my ammeter. Turn the crank _very_ slowly and notice that
the needle of the ammeter swings to and fro with each revolution of
the armature. That shows that you have not only a _dynamo_, but an
_alternating current_ dynamo.

[Illustration: Fig. 6]

"Now connect the binding posts _d_ and _e_ of this magneto (Fig. 6)
with a short piece of copper wire. Turn the crank and you notice that
this dynamo rings two electric bells. Turn slowly and you notice
that the alternations of the current are numbered by the strokes on
the bells. The hammer swings to and fro just as the needle of the
ammeter did. Each bell therefore receives one stroke of the hammer for
each revolution of the armature. Now try to turn the crank steadily
at the rate of one revolution per second. The armature is making
six revolutions, or cycles, per second and you now have not only
an alternating current dynamo but a _six-cycle alternating current
dynamo_. The lighting circuit used in our apartment is a _sixty_-cycle
alternating current. To be sure the armature of the dynamo which
generates that current revolves only once a second, but it carries
coils enough upon its rim to make that number of alternations.

"Now connect this telephone receiver with the binding posts _D_ and
_E_ of this magneto (Fig. 7). Unscrew the cap of the receiver. Move to
one side the iron diaphragm and turn slowly the crank of the magneto.
Notice that the diaphragm vibrates in time with the alternations of
the dynamo. Replace the diaphragm, screw on the cap, hold the receiver
to your ear and turn the crank as fast as you can. You will probably
be able to make about sixteen cycles per second. The receiver in that
case is giving forth a sound of the same pitch as a sixteen-foot closed
organ-pipe.

[Illustration: Fig. 7]

"Connect the telephone receiver to the binding posts _D_ and _E_ of
this magneto (Fig. 8), and by means of a belt connect the pulley to
this series of cog-wheels. Now you may turn the crank and readily make
the armature revolve at the rate of sixty cycles per second, and you
notice that you get the same tone that we heard in the dynamo room of
the power station and the same tone the telephone receiver gave when I
connected it to a coil in our apartment. The tone which is produced by
sixty vibrations per second is very nearly that of the _C_ two octaves
below middle _C_ on the piano. Try it along with the piano and you will
find it a little flat. This string on the piano is making sixty-four
_vibrations per second_.

[Illustration: Fig. 8]

[Illustration: Fig. 9]

"Now connect this miniature telephone switchboard lamp with the magneto
(Fig. 9) and turn the crank fast. The lamp lights up to full brilliancy
and you notice that the light is steady, although it is made by an
alternating current passing through the filament in one direction,
stopping entirely, and then passing in the opposite direction. The
filament has no time to cool off, provided you turn fast enough, but
try turning a little slower and you will notice the flickering of the
lamp."




III

THE AMMETER


[Illustration: Fig. 10]

At the last meeting of the Science Club so many questions were asked,
which the demonstrators could not answer, that a programme committee,
to whom such questions might be referred thereafter, was appointed.
It was made the duty of this committee to assign to various members
the task of searching for satisfactory answers, and when the material
was ready to be reported to the club, the programme committee
determined the time and order of presentation. I found that I had been
made an honorary member of this committee and that it was expected
that I should steer the committee. I told them that I accepted this
appointment with the understanding that the fellow who steers is always
the smallest man in the crew, and if they would do all the work I would
enjoy the honorary title of cockswain. Secretly, however, I appreciated
that this was in effect adding several courses to my already rather
heavy programme. I must, under the régime, direct a large number of
inexperienced students in library research, in laboratory research, and
in the art of giving demonstrations with apparatus and experiments to
audiences.

The most urgent questions, as also those which were next in the natural
order, concerned the _ammeter_. I told the committee to make that the
subject of the next meeting and to send to my laboratory on a certain
day the person or persons whom they might appoint to report upon it.

[Illustration: Fig. 11]

I find that the boys never come singly, but generally in pairs. When
the boys came they found lying upon the table an ammeter (Fig. 11).

I told one of them to take out the three screws in the front and remove
the face of the instrument. I had told the boys that the instrument
cost sixty dollars and that letting them open it was like letting
them open my watch. As soon as the face came off one of the boys
exclaimed that from my reference to the watch he had expected to see
very complicated machinery with many wheels, but from the exceeding
simplicity of the mechanism he could not see why it should cost sixty
dollars. I told him that although it was a fine piece of workmanship
it was fortunately very easy to understand, and I asked them if it
reminded them of anything else that they had ever seen. After a few
moments of reflection they agreed that it was very much like one of the
magnetos. "Well," said I, "where is the field?"

[Illustration: Fig. 12]

"Is this horseshoe arrangement a magnet?" they inquired.

"There is a compass needle right at your hand waiting to answer that
question," I replied. They immediately found that it was a magnet.
"Well," I said, "to be really sure that it is a magnet you must find
a portion of it that will _repel_ a portion of your compass needle as
well as other portions in both horseshoe and needles which attract each
other." Whereupon, they found that the portion marked _N_ (Fig. 13)
repelled the blue end of the compass needle and attracted strongly the
bright end of the needle, while the portion marked _S_ did the reverse.
"We will call _N_ and _S_ the poles of the magnet. This is simply a
steel bar magnet bent into the shape of a horseshoe."

[Illustration: Fig. 13]

"You told us," remarked one of the boys, "that steel magnets gradually
lose their strength. How then can this be correct as a measuring
instrument?"

"It is the purpose of the iron case to enable this magnet to retain its
magnetism, and if you will examine its field, as we did that of another
magnet upon a former occasion, you will find that although this is a
strong steel magnet its field does not extend outside of the iron case.
It is as though we could box up magnetism and keep it from escaping.

"Now if this is like the magneto, where is the armature? The spool-like
thing between the poles of the magnet looks just like the armature in
one of the magnetos.

"Yes, it has an iron core with a coil of insulated wire around it, and
you remember that when an electric current is sent around a piece of
iron, that iron is made into a magnet, and if it is a magnet it must
have poles. It is very delicately poised upon a pivot and will act
exactly like your compass needle, which is also a little magnet with
poles. I will send an electric current through the wire which surrounds
this armature, and you notice that the needle which it carries moves
to the right. Notice that the lower end of this armature acts like the
blue end of your compass needle in that it is repelled from the pole
_N_ of the field and is attracted toward _S_ of the field. In like
manner, the upper end or pole of the armature is repelled from _S_
and attracted to _N_ of the field. The blue end of the compass needle
is called its north pole because it points north under the magnetic
influence of the earth, and so we may call the lower end of the
armature its north pole.

"The electric current which I am sending through the armature comes
first through one ordinary 16-candle-power electric lamp which you
see lighted on this 'resistance board,' as it is called, and you
notice that the needle points to .5. This means that half an ampere of
electricity is passing through this lamp. I will now send the current
through a 32-candle-power lamp, and you notice that the needle points
to one, indicating that one ampere is required to light that lamp. But
what prevents the needle from going farther, and what brings it back to
zero each time?" The boys discovered a very small spring, like the hair
spring of a watch, coiled around the pivot of the armature. "So, then,
one ampere of electricity gives magnetism to this armature so that it
may pull against its coiled spring hard enough to carry the needle to
the point one. Twice as much electricity will give it magnetism enough
to carry it to two, and so on across the scale.

"The full name of this instrument is Ampere meter, which by usage
has been shortened to ammeter. It was named in honour of André Marie
Ampère, who was born at Lyons, in France, in 1775, the year our
Revolutionary War broke out. He died in 1836. When Oersted made his
famous discovery of the action of an electric current upon a magnetic
needle, in 1819, Ampère was in middle life (forty-four), and took up
the same line of research with great vigour. The next year, 1820, he
discovered what you will doubtless enjoy rediscovering now.

"You will notice that the binding posts on the bottom of this ammeter
are marked, one positive, +, and the other, negative -. The electric
current now enters the instrument by the post marked + and after
passing around the armature leaves by the post marked -. I will reverse
the connections and thus send the current around the armature in the
other direction, and you notice that its poles are now reversed. The
lower end which was formerly the north pole of the armature has now
become the south pole, as proven by the fact that it is repelled
from the south pole of the field and attracted to its north pole.
This carried the needle to the left, and inasmuch as the zero is in
the middle of the scale we may with this instrument both measure the
amount of current and tell its direction. You will recall that when
we connected the magneto with this instrument, it indicated that
the magneto sent the current first in one direction and then in the
other, which we call an 'alternating current.' But you notice that
the current which I am using in this laboratory flows continuously
in one direction. This is called the 'direct current.' We shall find
out how a dynamo may produce a direct current at another time. Let
us not forget, however, that we have repeated Ampère's discovery, and
found out that the direction in which we send the current around an
electro-magnet determines which end shall be its north and which its
south pole. If you will note carefully which way the wire is wound
around the armature you will see that when I send the current in at
the positive post it is passing around the north pole of the armature
opposite to the direction in which the hands of a clock move. If I
reverse the current it passes around the lower end of the armature
_in the same direction as the hands of a clock move_ and then this
end becomes a south pole. This is 'Ampère's rule,' and it is what
candidates for admission to college are very careful to learn.

"Before we replace the face of this ammeter I must call your attention
to a wire running by a short cut from one binding post to the other,
_s_ (Fig. 14). Suppose _a_ represents the wire around the armature.
Electricity, like water, goes more readily through a big conductor than
a small one and more readily through a short than a long conductor. If
_s_ and _a_ were water pipes, each having a stop-cock, we might easily
adjust the cocks so that one tenth of the water would go through _a_
and nine tenths through _s_. Or, indeed, without stop-cocks, the size
and length of _s_ and _a_ might be so apportioned that one tenth of
the water would flow through _a_ and nine tenths through _s_. This is
precisely the adjustment which has been made with reference to the flow
of electricity through this instrument. _s_ is called a 'shunt.' When
the shunt is out all the current goes through _a_ and when the shunt
is in only one tenth of the current goes through _a_. I have two other
shunts, each of which may be put in the place of _s_. With the second
only one hundredth of the current goes through _a_ and with the third
only one thousandth of the current goes through _a_. Thus I have an
instrument which will measure anything from one thousandth of an ampere
up to ten amperes.

[Illustration: Fig. 14]

"In this laboratory we pay about one cent for an ampere of electricity
for one hour. Twice as much coal must be consumed to furnish two
amperes as one, and twice as much coal must be consumed to furnish
an ampere for two hours as for one hour. Hence we need an instrument
which will keep account of time as well as amount of current. Such an
instrument we must look into next.

"Just before we pass to that, however, let me ask if you have ever
heard of a 'shunt-wound' dynamo. Can you guess from the way we have
just used the word 'shunt' what the expression could mean with
reference to a dynamo?" Without hesitation the boys told me that it
meant that the field and armature were wound parallel to one another,
as shown by diagram in Fig. 15. In which case the electric current
which the machine generates divides, part of it going around the
field and part around the armature. Another type, called series-wound
dynamos, is indicated by diagram in Fig. 16, in which case the electric
current goes through field and armature in succession. Under either of
these circumstances, how can the armature move with reference to the
field? The answer will appear in the next chapter.

[Illustration: Fig. 15]

[Illustration: Fig. 16]




IV

THE WATTMETER


We were able to maintain connections between the binding posts of the
ammeter and the movable armature of flexible wires because the armature
never moves more than one third of a revolution, but we now wish to
examine an instrument in which the armature must not only make a
complete revolution but must continue to revolve in the same direction
indefinitely. How are connections made so that an electric current may
pass from the fixed binding posts to the wire of the moving coil? I
will lift the cover off this instrument, which is called a wattmeter,
and let you find the answer to that question.

I sent through the instrument the current from a 32-candle-power lamp.
According to the ammeter, which was also in circuit, the amount was one
ampere.

The armature of the wattmeter revolved slowly and it was not long
before the boys reported that connections for the current were made
by strips of metal sliding on metal plates. The ends of the armature
wire were fastened one to one plate and the other to the other plate,
and the metal strips brush along over the surfaces of the plates. (That
is why they are called "brushes," I said.) And the brushes slide from
one plate to the other each time the armature makes half a revolution.
(That is, the brushes change the connection and thus change the poles
of the armature at the proper instant so that they are always attracted
to the poles of the field toward which they are moving.) This is called
a commutator.

Notice that while the ammeter was like the magneto in having a steel
magnet for its field, the wattmeter is like the dynamo in having
electro-magnets for both armature and field. Notice in the second place
that this instrument is an _electric motor_ since it is made to revolve
by an electric current. If it were made to revolve by some other power
it would generate electricity and would then be called a dynamo.
Indeed, let me tell you something which must at present be nothing
more than a puzzle to you. _Every machine, while it is being driven
by an electric current as an electric motor, is, at the same time,
acting as a dynamo to generate a current in the opposite direction._
Notice in the third place that this is a shunt-wound instrument. The
current which is sent into the instrument divides, and part of it goes
through the field, while part goes through the armature. Motors, as
well as dynamos, are either shunt-wound or series-wound. But notice
finally that the axle on which the armature is carried has a cyclometer
arrangement which keeps account of the number of revolutions. The
armature is going slowly enough for us to count the revolutions. With
watch in hand we found that it made one hundred and twenty revolutions
per minute. I next brought the current to the wattmeter through a
16-candle-power lamp and the ammeter, connected in series, showed that
half an ampere was passing. We counted the revolutions of the wattmeter
and found them to be sixty per minute.

Here, then, is a simple electric motor which will register the amount
of electricity we use. It will register the same amount whether we use
one ampere for one hour or half an ampere for two hours or two amperes
for half an hour. In any case this product is called _one ampere hour_.
But the words printed upon the dials of this instrument are not _ampere
hours_, but _watt hours_ and the name of the instrument is _wattmeter_.
This next requires explanation. Follow me in a little roundabout
journey and the matter will be readily understood when viewed from
another approach.

[Illustration: Fig. 17]

When we were estimating the energy required to climb the stairs of an
apartment house, we needed to take into account two factors, (1) our
weight and (2) the time which we took in climbing them. The amount of
coal burned, steam generated, electricity produced, to run our elevator
depends upon two factors, (1) its weight and (2) its speed. That idea
is fundamental. Let us get at it in still another way. Suppose we have
a mill pond, (Fig. 17, _A_). We construct a penstock _p_ and install
a water-wheel, _S_, to operate a mill. Our business increases and we
install more machinery in our mill and must have more power to run
it. We have two ways of getting it, (1) we may lengthen our wheel and
enlarge our penstock so that a greater weight of water will fall upon
the wheel, or (2) we may lengthen our penstock and move the wheel
farther down so that the water will fall upon the wheel with greater
velocity. It is just so with the electric current. Like water it is
driven on in its course by pressure. The unit for electric pressure is
called a volt. If we wish to drive the wattmeter or any other electric
motor twice as fast as now, we may choose whether we shall do so by
doubling the volts of pressure or by doubling the amperes of quantity.

The electric pressure on our mains is about one-hundred and ten volts.
We three together weigh 330 pounds. Our elevator brought us up stairs
at the speed of 100 feet per minute. It requires one horse-power to
raise 330 pounds 100 feet in a minute. The ammeter in the engine room
showed that 7 amperes of electricity were sent through the motor of the
elevator to bring us up. That is, seven amperes at 110-volt pressure
give one horse-power. In the office building across the street where
they use a 220-volt current 3-1/2 amperes are required to take us up
stairs at the same speed. It is necessary that the same amount of coal
be consumed to furnish the horse-power of energy whether we supply it
by means of seven amperes at 110 volts or 3-1/2 amperes at 220 volts.
You notice that the product is 770 in each case. The name given to
this product is _watts_. More accurately 746 watts of electrical power
are equivalent to one horse-power. The name of this unit commemorates
the famous inventor of the steam engine, James Watt (1736-1819). His
monument now overlooks the Clyde at his native town, Greenock, Scotland.

To light a certain lamp, to heat a certain laundry iron, to furnish a
certain amount of power for an electric motor, we must have a definite
number of watts. We may choose whether we will have it at high or low
voltage with correspondingly low or high number of amperes.

[Illustration: Fig. 18]

We will now connect with our laboratory current a 32-candle-power
lamp, an ammeter, and a wattmeter, all in series, Fig. 18, and in
parallel with these a volt meter. This last instrument indicates
the electric pressure. Its mechanism will be examined later. The
volt meter indicates 110 volts and the ammeter shows that one ampere
is passing. The filament in the lamp resists the passage of the
current. It gets quite hot and gives forth as much light as thirty-two
candles. Its resistance is just such that 110 volts of pressure send
one ampere through it. We will now take the reading of the wattmeter,
note the time and read it again later. One hour later its index showed
that 110 watt hours of electrical energy had been converted into light
and heat. This at the usual rate, costs 1.1 cents, one cent per hundred
watt hours or ten cents per thousand watt hours, called a kilowatt
hour. The more common 16-candle-power lamp costs about half a cent an
hour to operate. It requires one horse-power to keep fourteen of them
burning.

[Illustration: Photograph by Helen W. Cooke. Wattmeter]

I will now take you to see the wattmeter which measures all the
electric energy used in this building. You note down its reading and
the date and the next time you come we will read it again and thus
find out how much electricity has been used for electric lights, for
electric ventilating fans, for electric elevators, for electric ovens,
and electric irons in the school of household arts, for electric motors
to run lathes and other machines in the school of technical arts, for
electric experiments in my laboratories and lecture room, for electric
vacuum cleaners and, lastly, for pumping the pipe organ in chapel.

I saw by the boys' faces as they departed what would be the next
question that they would bring to me. Knowing, however, that the hour
was up, they were too polite to press it then.




V

THE ELECTRIC MOTOR


In a few days I received a telephone message, asking if I could appoint
an hour to meet the programme committee in my laboratory. I must
confess that my pleasure in these meetings had increased so much that I
was quite ready to slight other duties, if need be, to engage in them.
Moreover, since my business was education it was not difficult for me
to regard these meetings in the light of a duty quite as important as
my regular class instruction--perhaps more effective. At any rate the
boys and I managed to get together. May God forgive the man who essays
to teach boys, but does not love to be with them.

Of course at the last meeting of the Science Club every one wanted
to know how we ran a pipe organ by electricity. Moreover the
Electrical Show was coming on in the city, and cows were to be
milked by electricity, dishes were to be washed by electricity, rugs
and furniture were to be cleaned by electricity, and innumerable
distracting and distressing things were to take place. I told the boys
that really only two kinds of things were to be done by electricity at
the show, and if they would give me two one-hour appointments I would
furnish them with the key to the whole show. We might as well begin
to-day with the pipe organ question.

A pipe organ is operated by air. It has bellows which are simply one
form of an air pump. A boy is often employed to turn a crank which
works the bellows. Down in the basement underneath our pipe organ I
will show you how a half-horse-power electric motor takes the place of
a boy. We found a dark and dirty corner where a boy used to stand and
turn a crank every time æsthetically inclined people enjoyed an organ
recital in the room above. Science, which has not been given credit for
being _humanitarian_, put an electric motor into that dark corner and
sent the boy up stairs to hear the music. The motor _grumbled_ at the
dirt in the corner and compelled the janitor to keep it clean.

The electric motor, better than any device I know, enforces justice,
but never requires mercy, or at least rarely receives it. It comes
nearer than any other machine to paying back all that you put into it.
It is most economical when working up to its full capacity. I recommend
that you look it over carefully and after a few minutes tell me what
you have seen in it.

[Illustration: Fig. 19]

The boys said that it looked just like a dynamo. We must not forget
that it is a dynamo, but is here used as a motor by sending an electric
current through it. This fact, that a dynamo might be driven by an
electric current and serve as a mover of other machinery, was first
publicly exhibited in 1873 at the Vienna Exhibition, and by many
believed to have been discovered by accident at that exhibit. But why
does it look like a dynamo? It has a field whose magnetism is produced
by an electric current sent through coils of wire, and it has an
armature whose magnetism is likewise produced by the electric current.
If it were used as a dynamo, where would it get the electric current to
magnetize its field? From its own moving armature. Is it adapted for
direct current? Yes. It has a commutator and brushes. Is it shunt- or
series-wound? Shunt-wound, as shown by diagram in Fig. 20.

[Illustration: Fig. 20]

Suppose we treat the machine as a dynamo. Bring the ends of the line
wire together, thus, as we say, closing the circuit. By some external
force let us cause the armature to rotate and under the influence
of the magnetic field it will generate an electric current, part of
which will pass through the field and part through the line circuit.
We may adjust the relative amount of wire in field and line so that
any portion of the current we choose will pass through the field. The
amount of current it will generate depends, (1) upon the strength of
the field and (2) upon the speed of the armature. Its field, although
never entirely without magnetism, is very feeble at first, and hence
in the first instance a very small current will be generated in the
moving armature. This, however, will strengthen the field slightly, and
as the field is strengthened the armature will generate more current,
and thus by a mutual reaction the machine gradually "builds up" to full
strength.

[Illustration: Fig. 21]

When now we use the machine as a motor, an electric current must be
sent along the line wires in the opposite direction (Fig. 21) from
which it would come out of the machine when acting as a dynamo. It will
then be noticed that, although the direction of the current through
the field is the same, whether the machine is used as a dynamo or a
motor, the direction through the armature, when used as a motor, is the
reverse of that when used as a dynamo.

You may perhaps be able to notice that the amount of wire on the field
is considerably more than that on the armature. Now if you will trace
the wires carefully you will find that there is provided a way of
supplementing the wire of the armature with some more wire in what
is called the rheostat, Fig. 22. This wire, or portions of it, is
introduced into the armature circuit when the machine first starts.
When, however, the machine has started and the armature is moving
within the influence of a magnetic field, it plays the part of a dynamo
at the same time that it is acting as a motor. Two conflicting and
opposite electro-motive forces therefore exist in the armature at the
same time. In Fig. 22 the arrow _a_ represents the direction of the
electro-motive force which is impressed upon the armature, and the
arrow _b_ represents the counter-electro-motive force which the moving
armature develops.

[Illustration: Fig. 22]

This counter-electro-motive force, which develops while the machine is
in motion, makes it unnecessary to hold back the current longer by the
extra resistance of the rheostat and hence that is usually cut out.
Being used only for starting purposes and looking like a box, it is
generally called the "starting box." If now it was intended that this
motor should run at a constant speed, as is often the case, no other
governor would be needed than this counter-electro-motive force, for
whenever the machine begins to go faster, on account of reduced load,
its counter-electro-motive force increases as the speed and holds in
check the impressed electro-motive force. This acts very perfectly as
a governor, and motors operate with notoriously constant speed under
variable loads. But, of course, in this present instance the motor is
required to work at a variable speed. It must pump air slowly for the
soft passages of music, and it must work the pump to its utmost for the
very strong passages.

[Illustration: Fig. 23]

To understand how an electric motor may pump an organ and have its
speed automatically controlled, let us examine the diagram in Fig.
23. The motor _m_ causes the shaft _S_ to revolve, carrying the crank
_C_ around with it. The rod _r_ causes _a b_, the lower side of the
bellows, to rise and fall, this side being hinged at _b_. The side _b
c_, is fixed. When the side _a b_ is pushed upward by the crank rod the
valve _f_ closes and the air in the compartment _h_ pushes open the
valve _g_ and enters the compartment _j_. The upper side _d e_, of this
compartment rises as it is filled with air. Weights _K_, _K_, _K_,
rest on the top of this and air ducts lead from this compartment to
the pipes of the organ. The keys of the organ operate air cocks which
open and close the air ducts connected with the organ-pipes. A chain
connected with _e_ passes around the axle of the wheel _l_ and has a
weight _W_ upon its lower end. The wheel _l_ carries a strip of brass
_n_, which slides over metal points _p_, _p_, _p_, etc. The successive
points are connected by coils of wire to furnish resistance. This
series of coils is called a rheostat. The wires _t_ and _u_ form a loop
from the armature of the motor and connect this rheostat in series with
the armature. _u_ is connected with the brass strip _n_. Notice that
when the compartment _j_ is full of air and the side _d e_, is lifted
to its greatest height the strip _n_ is moved to the lowest point _p_,
and the electric current must pass from _u_ through all the resistance
of the rheostat in order to get back to the armature by the wire _t_.
This makes the motor go very slowly. When _d e_ sinks down, the strip
_n_ moves to the upper points _p_, and the resistance is reduced step
by step, enabling the motor to quicken its speed and pump faster as
more air is required.

Small motors in order to be effective must travel at high speed. This
motor when moving at its highest speed makes 1,800 revolutions per
minute. The bellows on the other hand needs to be large and move slowly
in order to be efficient. Hence the motor is not in reality connected
directly to the shaft _S_, but causes the shaft to revolve by means of
a series of pulleys and belts. The pulley on the motor is three inches
in diameter. It is connected by a flat leather belt with a wheel thirty
inches in diameter. When the motor therefore, makes 1,800 revolutions
per minute this wheel makes 180 revolutions per minute. The axle of
this wheel carries a small cog-wheel three inches in diameter and it
is connected by a chain belt with a cog wheel on the shaft _S_ (Fig.
23). Thus this shaft revolves thirty times per minute, that is, the rod
_r_ rises and falls each second. A pull of one pound on the rim of the
motor pulley will cause a pull of sixty pounds on the cogs of the wheel
upon the shaft _S_. If the second belt were leather, a sixty-pound pull
would cause it to slip on the smaller pulley. Hence the second belt is
a steel chain and the wheels have cogs, or sprockets, like a bicycle.

[Illustration: Fig. 24]

The organist before beginning to play closes a double-pole,
single-throw switch (Fig. 24), which sends the electric current to the
motor.

The motor pumps air until the bellows is full, and if the organist
delays playing, the strip of brass _n_ (Fig. 23) is carried below the
lowest point _p_, thus cutting off the current and stopping the motor.
As soon as he uses some of the air in the bellows, however, _n_ rises
and makes contact with the points _p_ and the motor starts.

This suggests that a somewhat similar thing is accomplished under
electric cars which have air brakes. An electric motor pumps the air
and compresses it in a tank. When the pressure reaches a certain
point, say sixty pounds per square inch, it automatically shuts off
the electric current from the motor which works the pump. But when the
motorman uses some of the air to apply the brakes to the wheels, and
the pressure in the tank falls below sixty pounds, the electric current
is again automatically turned on to the motor.

Of course if an electric motor can operate a pump to compress air it
may also work a pump to exhaust air. This is what is done in a vacuum
cleaner. The electric pump as it is called (which means a pump worked
by an electric motor), exhausts some of the air from a compartment in
the machine, and the atmosphere pressing in through nozzle and hose
carries dust from rugs and furniture with it into the compartment. The
best vacuum cleaners will produce a pressure of seven or eight pounds
per square inch, about half an atmosphere. This will remove dust from
the warp and woof of a rug better than our greatest hurricanes can when
the rugs are hung upon a line. There are three kinds of air pumps in
use with vacuum cleaners: (1) bellows, (2) rotating disk or fan, (3)
piston.

To milk cows by electricity is simply to apply the vacuum-cleaner idea
to the process, and, in general, doing things by electricity usually
means doing them by some machine that is made to go by an electric
motor. This then is the first key to the Electrical Show, and if you
will remember to look first for the motor it may remove much of the
mystery from some of the exhibits. In many cases it is not necessary
to have a complete electric motor, but simply an electro-magnet to do
the work. In booth No. 56 you will find a piano played by electricity.
Its keys are moving, but no hands strike them. There is no ghost at
work here. A little strip of iron has been placed upon the under side
of each key and a small electro-magnet is placed under that. It is
only necessary that wires should run from these electro-magnets to
two dry-battery cells and to push buttons, and a person far away may
play the piano. In reality, however, it is not a person but a roll of
punctured paper that opens and closes the electric circuits to these
various magnets underneath the keys.

It often happens that you see a person playing a pipe organ with his
keyboard far removed from the organ itself. In this case the keys
simply act as push buttons to close the electric circuit through
electro-magnets placed in the organ itself. These electro-magnets
operate the air valves of the various pipes.

[Illustration: Fig. 25]

You call at some apartment house where there is no hall boy, but a
row of push buttons labelled with the names of the tenants. You push
a button and the door which was locked opens apparently of its own
accord. To say that the door opens by electricity is only to add
mystery. What does happen is that an electric bell up in the apartment
rings in response to your push of the button, and in reply the tenant
pushes a button and the door is unlatched by an electro-magnet
concealed in the door casing (Fig. 25).

So I would say that the first key to the Electric Show or to the
multitude of electrical appliances which you meet in life is the
electro-magnet. Consider the motor as one illustration of its use.

If you are really to understand the Electric Show you should go
twice. I advise going with this key alone first and note down all the
applications of electro-magnets which you can find there. When you have
done so I shall be glad to have your report.




VI

APPLICATIONS OF THE ELECTRO-MAGNET


It became quite the rage now among the boys to find as many uses of
electro-magnets as possible. These were reported and explained to the
club and a list kept. This list included:

    1. Dynamo.
    2. Magneto.
    3. Ammeter.
    4. Wattmeter.
    5. Motor.
    6. Electric piano and organ players.
    7. Electric door openers.

Already noticed in the preceding pages, and the following:

8. _The Electric Spinner_ (Fig. 26).--A toy full of instruction. The
standard is a steel magnet which produces a magnetic field. Inside of
this is an electro-magnet which serves as an armature. Plainly visible
on its shaft is a commutator to which the electric current from a dry
cell is sent. This causes the armature to revolve and carry with it a
series of colour disks which may be adjusted so as to show what tint or
shade results from mixing colours in various proportions.

[Illustration: Fig. 26]

[Illustration: Fig. 27]

[Illustration: Fig. 28]

9. _The Electric Engine_ (Fig. 27).--This toy, with one dry battery
cell, develops power enough to run several other toy machines. The
diagram in Fig. 28 will make its plan of operation plain. _B_ is the
battery cell, _c_ the electro-magnets, _a_ an armature of iron. By a
rod this armature is connected with a crank on the axle which carries
the fly wheel _f_. Another crank, _d_, upon the same axle serves like
a push button to close the electric circuit at the right instant. The
wire _g_ from the battery cell encircles the electro-magnet _c_ and
then is connected to the iron base of the toy. When the crank _d_
touches the conductor _e_, which is a spring, the electric current
passes around the magnet, the magnet pulls the iron armature _a_, and
this gives an impulse to the wheel _f_ whose momentum carries it around
during that portion of the revolution when _d_ is separated from _e_
and _a_ is receding from the magnet.

It is customary to say that the circuit is closed through the base of
the machine, but this language requires interpretation. It means that
a way is provided for the electric current to pass through the base. A
person who is expert in language but not in electricity might expect us
to say "the circuit is open through the base."

[Illustration: Fig. 29]

10. _The Telegraph Sounder_ (Fig. 29).--This was a toy half a century
ago, but since the days of Samuel Finley Breese Morse it has become of
vast commercial importance. The Western Union Telegraph Company in 1909
had 211,513 miles of poles and cables, 1,382,500 miles of wire, 24,321
offices, sent 68,053,439 messages, received $30,541,072.55, expended
$23,193,965.66, and had $7,347,106.89 in profits. In the United States
more than 93,000,000 and in the world at large more than 600,000,000
messages are sent annually, and there are men still living who scoffed
at Morse's ideas as _impracticable_.

It is interesting to contemplate what would happen to the Stock
Exchange, to the newspapers, to the railroads, to the congressman
addressing his constituents from the floor of a legislative chamber, to
business in general, if the world were deprived of the telegraph.

A few years ago a telegraph despatch was sent from New York to San
Francisco, Tokio, London, and back to New York, 42,872 miles, in three
minutes less than an hour. Electricity can travel around the world in a
fraction of a second, the time was consumed in repeating the message.
I once sent a message from New York to New Haven to announce that I
was coming, and afterward took my train and reached New Haven in time
to receive my own message and pay the messenger boy. But I have never
lost faith in the beneficent results of Morse's labours.

Morse (1791-1872) was an artist and the first President of the
National Academy of Design. He was likewise a professor in New York
University and constructed his first experimental telegraph line upon
the University campus in 1835. His first public line was built from
Washington to Baltimore in 1844. The Western Union Telegraph Company
was incorporated in 1856. Of course the work of Morse rested upon that
of Oersted, in Copenhagen, who, in 1819, discovered electro-magnetism,
and upon that of Joseph Henry of Albany, who in 1827 first insulated
the wires.

[Illustration: Fig. 30]

The application of the electro-magnet to producing telegraphic signals
will be understood by referring to Fig. 30. _B_ is the generator of
an electric current--sometimes a battery and sometimes a dynamo. One
wire from this goes to the earth, _E_. The other wire goes through a
key, which, like a push button or a switch, serves to open or close
the circuit. This is normally closed when not in use. Through this
the current passes around the electro-magnet _S_, which attracts the
armature _a_, causing it to click against a metal stop, hence it is
called the sounder. From this the current passes along the line wire to
a distant station and there through the sounder and closed key to the
earth. There is likely to be a generator at each station. The current
must run continually through the system. If a battery is employed, the
copper sulphate, or gravity cell, to be described later, is chosen,
because it will endure continued usage better than any other.

The operator, in sending signals, opens the circuit, the magnets cease
to hold down the armatures, and they are raised by springs and strike
against metallic stops above. It is customary to say that the circuit
is completed through the earth. This statement misleads some persons
into imagining an electric current capable of corroding water pipes
and decomposing chemical compounds, passing through the earth between
stations.

[Illustration: Photograph by Helen W. Cooke. Testing the Telegraphy
Outfit]

Perhaps it will help to a better understanding of the truth if we
think of a city pumping water out of the ocean, say to fight fire,
and disposing of it again into the ocean. The ocean currents thus
produced are not likely to be destructive. Indeed, just as we measure
height from the ocean level as zero, so we measure electric pressures
as from the zero level of the earth's electrical state.

[Illustration: Fig. 31]

The key used by telegraphers is represented in Fig. 31. It has
connected with it a switch to keep the circuit closed when the key
is not in operation. The Morse code of signals consists of dots and
dashes, when printed, as follows:

    a . -
    b - . . .
    c . .  .
    etc.

Operators learn to read the message by the intervals between sounds. A
dot consists of two taps of the sounder with a short interval between,
and a dash consists of two taps with a longer interval between. One tap
of the sounder is caused by its descending upon the metal stop below
and another by its rising against the upper stop.

Telegraph sounders are operated on about a quarter of an ampere of
current if from a battery circuit, or on about one tenth of an ampere
from a dynamo circuit. The dynamo circuit is supplied with more volts
of electric pressure, and hence its power is ample to cause the
armature to strike the metal stops hard enough to be heard by the
operator.

For example a battery circuit may supply to the sounder a current with
these characteristics:

    2 volts × .25 amperes = .5 watts,

while a dynamo circuit may give:

    6 volts × .1 ampere = .6 watts.

Telegraph line wires are usually bare, the insulation being merely the
glass knobs at the poles. Clean water is a very good insulator but
dirty water is a fairly good conductor. A wet telegraph pole may bring
so much current to earth as to prevent all sounders on the line from
operating. Hence the line is separated from the poles by glass. The
poles are about one hundred and thirty-two feet apart, making forty to
the mile. The wires are usually galvanized iron one sixth of an inch
in diameter. Copper conducts six times as well as iron, and is now
replacing iron in the lines.

Morse laid a submarine telegraph line in New York Harbour and suggested
a cable across the ocean. But that gigantic undertaking had to await
the masterful intelligence of Lord Kelvin and the indomitable will of
Cyrus W. Field. A submarine cable was laid across the Strait of Dover
in 1850. It was cut by the anchor of a fisherman a few hours after
it was laid. The first attempt to lay a submarine cable across the
Atlantic Ocean was made in 1857. Two ships of war, the _Agamemnon_ of
Great Britain and the _Niagara_ of the United States, engaged in this
undertaking. Three hundred miles had been laid when the cable parted
where the ocean was more than two miles deep. William Thomson was on
board the _Agamemnon_ as electrical expert. He went home to study and
improve the methods. The next year, 1858, the _Agamemnon_ and the
_Niagara_ met in midocean each with a portion of the cable on board.
The splice was made, and the _Agamemnon_ started toward Ireland and the
_Niagara_ toward Newfoundland. When six miles apart the cable broke.
The ships met again, made a new splice and again started in opposite
directions. They laid eighty miles and the cable parted a second time.
They met again, spliced and laid two hundred miles when it parted for
the third time. They met a fourth time, made the splice and succeeded
in laying the first cable from Ireland to Newfoundland on August 5,
1858.

In a few weeks the insulation failed and no more messages could be
sent. Seven years were spent in studying the problem, and again in
1865 the _Great Eastern_, a mammoth ship, started to lay the cable.
William Thomson was again on board as the expert. When twelve hundred
miles had been laid the cable parted in deep water. Three times the
cable was grappled and brought part way to the surface and lost again.
The _Great Eastern_ returned to land. The next year, 1866, the _Great
Eastern_, having on board William Thomson (Lord Kelvin), Mr. Canning,
the engineer of the expedition, and Captain Anderson, in command,
laid the cable which has worked successfully ever since. Thomson,
Canning, and Anderson were knighted as a result of their labours. Sir
William Thomson (1824-1907), afterward Lord Kelvin, is credited with
having solved the difficult electrical problems connected with this
enterprise. Cyrus W. Field (1819-1892), born in Stockbridge, Mass.,
helped to secure the many millions of dollars necessary to carry the
work to completion.

There are now seventy-three cables connecting Europe and America, and
two across the Pacific Ocean. Cable rates are: New York to England,
France, Germany, or Holland twenty-five cents a word, to Switzerland
thirty cents a word, and to Japan one dollar and thirty-three cents a
word.

[Illustration: Fig. 32]

The boys were kept very busy now looking up historical and biographical
sketches, as well as working up the many applications of the
electro-magnet. The next to be reported was:

11. _The Relay_ (Fig. 32).--Telegraphing from 3,000 to 10,000 miles
under the ocean is full of difficulties not now to be explained.

Of course when we attempt to telegraph many miles upon land we
find that the resistance of the wire cuts down the strength of the
current so that it will not move the sounder. This, however, is
readily obviated by the relay devised by Morse. It simply serves as
an automatic key to close a circuit. A diagram will make this clear
(Fig. 33). Suppose the line wire to be very long and on account of its
resistance the current is too feeble to operate a sounder. It is likely
to be about .025 ampere where the local sounder may require .25 ampere
or ten times as much. It is easily possible to wind a magnet (Fig. 33),
_R_, such that .025 ampere will close the armature _a_, so that it
may complete a local circuit when it would not make noise enough for
a sounder. _B_ may represent a local battery of any desired strength
which may operate the sounder _S_ of that station as loudly as may be
desired.

[Illustration: Fig. 33]

[Illustration: Fig. 34]

12. _Annunciator_ (Fig. 34).--We live in a fifth-floor apartment.
When we push the button to call the elevator a No. 5 appears in the
annunciator in the elevator car. This tells the elevator boy where
the call comes from. Take out two or three screws and the annunciator
opens, revealing a series of electro-magnets like the one shown in Fig.
35. When an electric current passes around the coil it pulls back an
iron catch and allows a number to drop so as to show through a small
window. The elevator boy, having noted that the call is from the fifth
floor, pushes up the number and the iron catch holds it until the coil
is magnetized again by an electric current.

[Illustration: Fig. 35]

[Illustration: Fig. 36]

[Illustration: Fig. 37]

The annunciator has a bell to call attention. A cable of six wires
enters this annunciator (Fig. 36). One wire goes direct to the bell
and the other five reach the bell through the separate coils of the
electro-magnets which control the drops. But how are electrical
connections made between a moving elevator car and the push buttons on
various floors? The diagram in Fig. 37 shows this in elevation. _B_
represents a battery of several dry cells located in the basement. One
wire from it runs direct to the push buttons 1, 2, 3, 4, 5, located
upon the five floors of the house. The other wire from the battery,
together with wires from each of the five push buttons, all run to a
point, _A_, half-way up the elevator shaft. Here the six wires are
gathered into a cable long enough to reach either to the top or the
bottom of the elevator shaft. The other end of this cable enters the
elevator car and runs to the annunciator. The wire from the battery
goes direct to the bell. The wires from the various push buttons go
through correspondingly numbered electro-magnets to the bell. When,
therefore, we pushed the button on the fifth floor, we closed the gap
in the electric circuit at that point. The current came up from the
battery, passed through the button, went down the cable to the car,
went through electro-magnet No. 5, went through the bell, and returned
direct to the battery, thus completing the circuit. Annunciators are
used about buildings to call other attendants, besides the elevator
boy. They are likewise used in burglar alarms to inform the householder
which door or window is being forced. They are used in the fire
department to tell what part of the city the call came from.

[Illustration: Fig. 38]

13. _The Electric Bell and Buzzer_ (Fig. 38).--So common a thing as an
electric bell really belongs to the present generation. Bells were
either novelties or toys when I was your age. They cost then many times
what they do now and then were poorly made. Nobody dared to trust them
for front-door bells. It was necessary to have a card permanently
posted over the push button saying, "If the bell does not ring, knock."
In those days batteries were troublesome to care for, houses were not
wired when built, and no one had learned the art of concealing the
wires neatly.

The buzzer is simply a bell minus gong and hammer. Those shown in Fig.
38 ring well on a single dry cell. A cell costing twelve cents operated
one for two years while it was used as a call bell from dining room to
kitchen, the current required being .15 ampere.

[Illustration: Fig. 39]

[Illustration: Electric Bell]

The connections are shown in the diagram (Fig. 39). Suppose the current
to enter at the binding post _a_, pass around the magnets _b_ and
then to the post _c_. The armature _d_ normally rests against the
post _c_ and the current finds its way along this to the post _e_ and
thence back to the battery. But as soon as the current passes, _b_
becomes a magnet and pulls the armature _d_ away from the post
_c_, thus breaking the circuit, when _b_ ceases to be a magnet and a
spring pushes the armature _d_ back against the post _c_ to repeat the
operation. The armature _d_ carries a hammer which strikes the gong
_f_. If the wire, which is usually connected with the binding post _e_,
is connected with the post _c_, the "clatter" bell is changed to a
"single-stroke" bell, and if the gong and hammer are removed the "bell"
is changed to a "buzzer."

[Illustration: Fig. 40]

In the case of the buzzer, by changing the length of the armature or
by weighting it, we may change the time of its vibrations and its
tone. The connections between battery push button and bell form a
complete circuit. In Fig. 40 _B_ represents a battery, usually of dry
cells, _B'_ represents the bell, and _P_ represents the push button.
The electric circuit is "open," (that is, there is a break in the
conductor) at _P_ until some one "pushes the button," that is, simply
pushes against a spring so as to cause a piece of metal to bridge the
gap in the conductor. Then we say the circuit is "closed."

[Illustration: Fig. 41]

[Illustration: Fig. 42]

Push button devices and switches are innumerable. In every case they
are simply devices for pushing one piece of metal against another
and completing the circuit for an electric current. Every one should
unscrew and examine a few of them, both for the pleasure of seeing how
they work and to learn how to make them work when they sometimes fail.
Not only in bells but in all other instruments where electro-magnets
are used, the magnets are placed in pairs, fastened together upon an
iron base. They are wound so that the free ends are made opposite poles
by the electric current. Like a horseshoe magnet, they form one magnet.
The two poles thus placed are mutually helpful and each is stronger
than it would be if separated from the other.

[Illustration: Fig. 43]

14. _Electric Clocks, Self-winding Clocks, Programme Clocks._--A
pretentious-looking thing which appeared like a dish pan with a glass
bottom was opened by the boys and found to be the simplest of all
clocks. It had an electro-magnet like that in Fig. 44. A strip of iron
acting as an armature across the free ends of this magnet, pushed like
a finger against the cogs of a wheel. This wheel was on the axle of
the minute hand and it had sixty cogs. The electric circuit was closed
through the magnet for an instant each minute and the armature pushed
the wheel ahead one cog. Thus it made one complete revolution in an
hour. A train of four other cog-wheels caused the hour hand to trail
after at one twelfth the speed of the minute hand. This machinery made
simply a small handful in an eighteen-inch stamped-metal "dish-pan"
costing fifteen dollars.

[Illustration: Fig. 44]

A self-winding clock was opened and found to contain two dry battery
cells, an electro-magnet which operated very much like that of a
"clatter" bell, the hammer like a finger poking against the cogs of
a wheel. Once an hour the long hand closed the circuit through the
battery and the magnet and its armature swung back and forth long
enough to give the cog wheel one complete revolution and wind a
spring, which it carried upon its axle. This spring kept the clock
running one hour, until the next winding.

[Illustration: Fig. 45]

The programme clocks which were examined were self-winding clocks, but
were connected by wires to the master clock which corrected them each
hour. Each time the long hand of the master clock came to twelve it
closed an electric circuit through all the clocks in the system. In
each clock the current passed around an electro-magnet and caused it to
pull an armature against a metal stop and set each long hand exactly at
twelve. This master clock is sometimes situated many miles away and may
correct the time for a whole city. Thus a master clock at Washington,
D. C., furnishes standard time to all parts of the United States. The
master clock which we examined also closed the circuit at proper
intervals through a series of programme bells placed in the various
class rooms, and these called and dismissed classes automatically.

15. _Watchman's Time Detector_ (Fig. 45).--This is a device to compel
a watchman to make his appointed trips. Push buttons or switches are
distributed about the building at various points, and it is made his
duty to close the circuits at these points at stated times. When he
does so, the fact is recorded by electro-magnets puncturing, or, in
some way, marking a revolving time card in the clock.

[Illustration: Fig. 46]

16. _Circuit Breakers_ (Fig. 46).--Electro-magnets are used to open
switches and thus protect dynamos and other machines against a larger
electric current than they are able to carry. The switch is held
closed by a spring which, by an adjusting device, may be tightened or
loosened. A dynamo which we examined had its circuit breaker adjusted
so that it would remain closed if any current under 1500 amperes
passed, but if a greater current than that passed it would strengthen
the magnet sufficiently to open the switch and thus break the circuit.

17. _Separating Iron from Ore._--In 1897 Edison first proposed to
use an electro-magnet to separate iron from crushed earth. Fig. 47
represents the process. _E_ is an electro-magnet. _S_ is the stream of
crushed ore containing iron. Gravity would cause all the material to
fall into bin _A_, but the electro-magnet _E_ pulls that portion of the
material which is magnetic to one side so that it falls into the bin
_B_.

[Illustration: Fig. 47]

[Illustration: Fig. 48]

18. _Lifting Magnets._--Electro-magnets are made for use with hoisting
apparatus to save the trouble of manipulating grappling hooks, etc.
They may lift barrels and boxes of iron, the wood of the barrel or
box being transparent, we say, to the magnetic influence. That is, the
magnet will attract iron through the wood just as light will shine
through glass. Such magnets are used to pick up from the bottom of
the sea cases of hardware from wrecked ships. (See the accompanying
illustration, Fig. 48.) In such cases the electric conductors which
lead to and encircle the magnets must be well insulated from the water
of the sea, otherwise the electric current would take the shorter
path from one line wire through the sea water, which is a fairly good
conductor, and back by the other line wire, rather than go the path of
greater resistance around the magnet. Electro-magnets are coming into
use in foundries, etc., for lifting heavy iron castings.

[Illustration: Fig. 49]

19. _Electro-Magnet on Starting Box._--As was explained under _electric
motors_, a starting box is simply a series of resistance coils _r_,
_r_, _r_, _r_, _r_, in Fig. 49. When the motor is not in use the switch
_l_ rests upon the point 1 and no electric current passes. When the
switch is moved to point 2, the current entering at _a_ passes to the
pivot of the switch and up the metal strip _l_ to the point 2, then
around the series of coils, _r_, _r_, _r_, _r_, _r_, to the post _b_
and thence back to the generator. As the switch is moved to the right,
the current passes through less and less of this resistance until, when
it reaches point 7, all the coils of resistance are "cut out," that is,
they are not in the path of the current. Now the motor has reached its
full speed and is developing enough counter-electro-motive force to
protect itself against too much current. Through a shunt, however, a
portion of the current passes from _a_ to _b_ around the electro-magnet
_e_, the two poles of which are presented to the metal strip _l_, which
must be of iron. This magnet holds the switch over so long as the
current is on, but when the current is cut off, by opening a switch in
the line wire, _e_ ceases to be a magnet and _l_ is carried back to
point 1 by a spring. Thus an extra resistance must always be in circuit
when the motor is first started. Those who start motors are expected
to move the lever _l_ of the starting box slowly from point to point,
pausing a second or two on each to give the motor time to acquire
proper speed for its protection. How too great a current would "burn
out" a motor will be explained later.

The motor man handles a lever for starting his car, which works like
that of the "starting box." His "starting box," however, is called a
"controller." Although it accomplishes the same result as the starting
box it has a wholly different and vastly more complex mechanism than
that already described.

The elevator boy, who runs our electric elevator, handles a lever which
also does the same thing through far different mechanism. Indeed, in
his case electro-magnets are used to prevent him from cutting out
resistance too fast if he should move his lever too quickly.

20. _Starting Switches for Electric Elevators._--The motor man has
to be instructed particularly how he should handle the lever of his
controller, and he is trusted to follow his directions to some extent,
however lacking in intelligence and integrity he may be. But the
elevator boy receives scarcely any instructions about his machine, and,
indeed, his machine has been constructed pretty nearly "foolproof." It
will automatically correct his errors of management. If he throws the
handle from one extreme to the other, all resistance cannot be thrown
out instantly, but this is accomplished by a series of electro-magnets
closing one switch after another and thus cutting out resistance
gradually.

21. _Arc Lamp Feed._--As will be explained later, an arc lamp must
have its carbons touching one another when the current is first thrown
on, and then the carbons must be drawn apart from a quarter to half an
inch. The upper carbon is lifted away from the lower one by a portion
of the current passing by means of a shunt around an electro-magnet.

[Illustration: Fig. 50]

[Illustration: Fig. 51]

[Illustration: Fig. 52]

22. _Volt meter._--The volt meter measures the pressure of an electric
current. The volt meter which we examined looked outside like our
ammeter, and when we removed the face it appeared inside like an
ammeter. There was the steel magnet of horseshoe shape to furnish a
field (Fig. 51), and there was an electro-magnet poised between its
poles for an armature. The armature in the volt meter, however, had
wound upon it finer wire and more of it than was the case in the
ammeter. There was no shunt wire in the volt meter as there was in
the ammeter. We connected in series a fluid cell (to be described
later), the ammeter, and the volt meter (Fig. 52). The ammeter shunt
was removed so that all the current went through its armature. The
volt meter needle went to one which was two thirds of the scale (Fig.
53), and the ammeter needle indicated .016. That is, this particular
cell can push sixteen thousandths of an ampere through the resistance
of this volt meter, and .016 ampere passing through the armature of
this volt meter will magnetize it sufficiently to move it against its
spring, say sixty degrees.

[Illustration: Fig. 53]

[Illustration: Fig. 54]

[Illustration: Fig. 55]

We put into the circuit a lot more fine wire for resistance, _R_ (Fig.
54), so that the volt meter needle went only half as far as before,
that is to .5. The ammeter indicated only half as much as before,
that is .008 ampere. We put in resistance enough to bring the volt meter
needle down to .25 and the ammeter indicated one quarter of
the original current. We put in less resistance, bringing the volt meter
needle to .75, and the ammeter indicated three fourths of the
original current. Evidently the volt meter is merely an ammeter with
a different scale marked upon its card. With a pen we marked upon the
card of the volt meter a true ammeter scale (Fig. 55).

[Illustration: Fig. 56]

In order to understand the volt meter, let us turn our attention for a
moment to Fig. 56. I have arranged the water tank _T_ at such a height
above the faucet _F_ that when the faucet is opened one quart of water
will flow in a minute. If I partially close the faucet, making the
opening one half as large (that is, offering twice the resistance to
the flow), half a quart will flow in a minute. If I make the resistance
four times as great only one quarter of a quart will flow in a minute.
It is evident that I could arrange a scale underneath the handle of the
faucet to indicate the quantity of water flowing, just as the ammeter
and volt meter indicate the quantity of electricity which flows. If now
that much is understood, it will be easy to learn how the water faucet
may be used to measure water pressure and the volt meter in like manner
used to measure electric pressure.

Having set the faucet so that a quart will flow per minute, let us put
on a longer tube _p_, and move the tank up to another shelf so that the
distance from the water level in the tank to the faucet is twice as
great as before. Under the increased pressure water runs through the
faucet twice as fast and we now get two quarts per minute.

I purposely placed the tank out of sight behind a partition so that you
might practise judging the water pressure by the flow at the faucet.
We cannot very well talk about pressure in quarts. We might talk about
it in pounds, but if we used this apparatus much we should probably
get into the habit of talking about the pressure from one shelf, two
shelves, three shelves, etc.

In order that the pressure might remain nearly constant during the
experiment we would probably introduce resistance (that is, partially
close the faucet) so that the water level should not fall much. We
might, for example, set the faucet so that half a pint would flow in
a minute when the tank was on the first shelf. Then a pint per minute
would flow when the tank was on the second shelf and one and a half
pints per minute when the tank was on the third shelf, etc. Thus we
should infer the pressure by measuring the quantity.

One more illustration and the case will be clear. To save the trouble
of measuring the quantity of water which flows through the faucet,
suppose I introduce the device represented in Fig. 57. _W_ is a small
water wheel comparable to the armature of the volt meter. It carries a
pointer which moves over a scale just as in the case of the volt meter.

[Illustration: Fig. 57]

It has a spring coiled around its axle which tends to keep the pointer
at _0_, as in the case of the volt meter. The tank is placed upon the
first shelf, the faucet is fixed so that a small amount of water flows
and the needle moves to a certain figure upon the scale. We will mark
this point one and call it "first-shelf pressure." The tank is lifted
to the second shelf and the index moves to another point, which we will
mark two and call it "second-shelf pressure." The tank is lifted to the
third shelf and the index moves to a third point, which we will mark
three and call it "third-shelf pressure," etc.

Ordinarily we measure water pressure with an instrument which allows
no water to run to waste, but in measuring electric pressure by the
volt meter some current must pass through the instrument, just as in
the case of our water-wheel illustration in Fig. 57. We put in large
resistance so as to make this current as small as possible, while we
let enough pass to move the armature.

[Illustration: Fig. 58]

Now let us return to the volt meter itself. By referring to Fig. 55,
we see that it requires .024 ampere to move the needle of the volt meter
clear across the scale, and we have found that one fluid cell was
able to send enough current through the resistance of the armature to
move the needle two thirds of the way across the scale. At this point
we find Fig. 1, which might be read "one-cell pressure." We prefer to
commemorate the name of one of the workers in the field of electricity
and call this pressure a "volt" after Alessandro Volta (1745-1827),
born at Como, Italy. It is the electric pressure which is produced by
one fluid cell of a certain kind. We say, then, that one volt pushes
through the resistance of this armature .016 ampere. Half a volt would
push through the resistance of the armature half as much current or
.008 ampere. At this point we put .5. Thus each of the figures in the
lower row (Fig. 55) shows what part of a volt is required to send
enough current through this particular armature to move the needle to
that point.

[Illustration: Fig. 59]

We found out how much wire was wound upon the armature and put exactly
the same amount in the outside resistance, _R_ (Fig. 59). The needle
now showed that one volt is able to push through twice the resistance
of the armature only half as much current, and the needle stopped
at .008 ampere. If this were to be the resistance in the volt meter
circuit one volt should stand under .008 ampere and two under .016 and
three under .024. It is evident then, that, if we know the internal
resistance of a volt meter, we may make it capable of measuring greater
electrical pressures by adding the proper amount of resistance. By
putting at _R_, (Fig. 59) nine times the internal resistance of the
instrument, thus multiplying the total resistance tenfold, the figures
upon the scale of volts may be read as whole numbers from one to
fifteen. In this case it will require fifteen cells to push the needle
clear across the scale and ten cells to push it two thirds of the
way across. If now we add enough external resistance to multiply the
resistance of the armature a hundred fold it will require 150 volts to
push .024 of an ampere through the armature and pull its needle clear
across the scale. In this case the figures upon the scale of volts are
multiplied by one hundred and read from ten to one hundred and fifty.
Such a scale would adapt this volt meter for use with our 110-volt
lighting circuit. Volt meters are made with a series of such external
resistances, called "multipliers," attached so that they may be easily
thrown into the circuit.

It is evident that we need some term so that we may speak of quantities
of resistance. This need has given rise to a unit of resistance called
an ohm, after George Simon Ohm (1789-1854) born at Erlanger in Bavaria.
Two inches of No. 36 German silver wire, such as is wound upon the
armature of this volt meter, gives one ohm of resistance. There are 125
inches of this wire upon the armature. Its resistance is, therefore,
62.5 ohms, and we may, therefore, say that one volt of electric
pressure can push through 62.5 ohms of resistance .016 of an ampere of
current. Ohm discovered this relationship in 1827, and formulated it
as follows:

    volts/ohms = amperes (not, however, using these words).

    (1 volt)/(62.5 ohms) = .016 ampere.

    62.5) 1.0000 (.016
             625
            ----
            3750
            3750
            ----

This is called Ohm's law, as every candidate for college admission will
hear and hear again.

[Illustration: Fig. 60]

Volt meters and armatures for the alternating current have
electro-magnets for their fields as well as for their armatures. Such
instruments are equally well adapted for either direct or alternating
currents. For when the current reverses its direction it reverses in
field and armature alike, and thus a repulsion between like poles is
maintained. Such an instrument, however, cannot respond to as slight
a current as those previously described, since they must consume some
energy in both field and armature.

23. _Telephone Receiver_ (Fig. 61).--It requires a stretch neither
of the imagination nor of the truth to call a telephone receiver an
electro-magnet, although perhaps it has never been called that before.
We took it apart and found that it consisted of a steel-bar magnet _m_
(Fig. 62), with a small spool of wire _w_ around one end of it. The
ends of the wire on the spool run along inside the hard rubber shell
to the two binding posts _a_ and _b_ at the other end. A disk of sheet
iron _S_ is held in the large end of the case very near to, but not
quite touching, the end of the magnet. When an alternating current is
sent through the wire upon the spool it causes rapid changes in the
strength of the magnetic field, if not reversals of the poles of the
field, and the iron disk is made to vibrate, keeping time with the
alternations of the current.

[Illustration: Fig. 61]

[Illustration: Fig. 62]

In this laboratory we have seen that our current has sixty alternations
per second. When it is connected with the receiver the disk, therefore,
makes sixty vibrations per second, and produces a tone which has very
nearly the pitch of C two octaves below the middle C upon the piano.

24. _Spark Coil_ (Fig. 63).--The automobile spark coil which we have
already used is an electro-magnet. The battery sends a current through
wire coiled around an iron core. At one end of this iron core is an
iron armature which is made to vibrate in precisely the same manner as
the armature of an electric bell. This makes and breaks the current and
causes rapid changes in the strength of the field. A rapidly changing
magnetic field may be used to develop electricity in a conductor, as we
have already seen in the case of the dynamo.

[Illustration: Fig. 63]

How it is used in the automobile spark coil will be shown later. It is
sufficient now to mention it as a case of a magnetic field produced by
an electric current passing through a wire coiled around an iron core,
or, in short, an electro-magnet.

Induction coils, Ruhmkorff coils, and transformers, to be described
later, are closely related to this. They all create magnetic fields in
the same way and are all electro-magnets.

[Illustration: Fig. 64. Transformers]




VII

ELECTRIC HEATING


It was Washington's birthday. The schools were to have a holiday and
the Science Club was to hold a special, open meeting at which I had
been asked to present the subject of electricity in the household. I
replied to the programme committee that that was too large a subject,
but that I would talk upon electric heating. I warned them, however,
that it would be a dry study, and not an entertainment. They replied
that the father of his country had been born at a time of the year
when the weather was unfavourable to outdoor sports, and that February
usually found them acclimated to vigorous study. Neither they nor their
friends objected to study if it seemed to have a motive.

I found an audience composed of old and young, men and women, girls and
boys. Most of them had left school--many of them because their teachers
thought they were incompetent to continue.

[Illustration: Fig. 65]

Not far from here is "a wheel in the middle of a wheel ... as for their
rings they are so high that they are dreadful ... and the spirit of the
living creature is in the wheels." Those wheels are now sending the
electric current to this room for our experiments. I propose to show
that we convert electricity into heat by offering resistance to its
flow. Experience teaches us that resistance to motion always produces
heat. At Niagara Falls thousands of tons of water descend at the rate
of one hundred and sixty feet in three seconds. When the water reaches
the bottom of the falls, it is moving a little faster than a mile a
minute. The resistance which this mass meets after its fall retards its
motion and generates heat.

Hundreds of meteors fall into our atmosphere daily, travelling a
thousand times as fast as the waters of Niagara Falls. The resistance
to their motion, which our atmosphere offers, heats them white hot,
melts them, vaporizes them, burns them up, so that very few of them
reach the solid earth in a solid condition.

An iron spile driver, measuring two cubic feet, weighs about half a
ton. When it falls sixteen feet upon the end of a spile it is moving
at the rate of twenty miles an hour. The energy of this moving mass
depends upon both its weight and its velocity, and when its motion is
arrested by the spile that energy of motion is largely converted into
heat energy, from which both the spile and the spile driver get hot.

A piece of iron may be made red hot by pounding it with a trip hammer.

Count Rumford found, in 1798, while boring cannon in the arsenal at
Munich, that the resistance which the iron offered to the motion of the
boring tool furnished heat enough to boil water.

Seven hundred and seventy-eight foot pounds of mechanical energy when
converted into heat would raise one pound of water (one pint) one
degree. This is called the British thermal unit. The spile driver,
weighing 1000 pounds, falling 16 feet upon a spile, produces heat
enough to raise 1 pint of water 20 degrees.

[Illustration: Fig. 66]

Here are two binding posts, _a_ and _b_, 8 feet apart (Fig. 66),
connected by copper wires with the dynamo circuit. The volt meter
indicates 112 volts of pressure. I will close the circuit by stretching
between _a_ and _b_ 8 feet of No. 24 iron wire. (This wire is about the
thickness of a common pin.) The iron wire offers resistance to the flow
of the electric current, thereby producing heat--heat enough as you see
to make the wire white hot, indeed heat enough to raise it to something
over two thousand degrees Fahr., for now you see it has melted.

We will put in a fresh piece of wire and connect also the ammeter
in the circuit (Fig. 67). As I close the circuit the needle of the
ammeter at first indicates 20 or 30 amperes, but in a second drops to
8 amperes, and remains there a second until the wire melts and falls
apart. One hundred and twelve volts of electric pressure are able to
push 8 amperes of electricity through this wire when hot.

[Illustration: Fig. 67]

    (112 volts)/(14 ohms) = 8 amperes

    112 volts × 8 amperes = 896 watts

    746 watts = one horse-power

Hence it required about one and one fifth horse-power to melt the wire
in a second, and the heat produced was a little less than one British
thermal unit, a unit much used by engineers.

     1 pound raised 1 foot = 1 foot pound

     550 foot pounds per second = 1 horse-power

     778 foot pounds (1.4 H.-P.) = 1 B. T. U. (British thermal unit) =
     heat required to raise 1 pound of water 1° Fahrenheit

     1 volt × 1 ampere = 1 watt

     746 watts = 1 horse-power

In order to hold back 112 volts of electric pressure so that not more
than eight amperes of electricity should pass, the iron wire must have
offered about 14 ohms of resistance.

The behaviour of the ammeter needle showed that the wire offered very
much less resistance when cold than when hot. Indeed eight feet of No.
24 iron wire offers about one and one third ohms resistance when cold,
hence heat had increased its resistance to the passage of the electric
current tenfold.

This piece of iron wire offered resistance to the flow of the electric
current. It offered resistance to the motion of the dynamo. This
offered resistance to the steam-engine which drives the dynamo. This
caused the governor of the engine to open and pass more steam from
the boiler. This reduced the pressure at the steam gauge. This caused
the fireman to shovel more coal into the furnace. The heat of the
burning coal melts the wire, but it does it only after several changes.
First, it is converted into mechanical energy in the steam-engine with
great loss--about nine tenths being lost. Second, it is converted
into electrical energy by the dynamo, with some loss, and, third, it
is conducted to the iron wire and converted back to heat with still
further loss. It is evident that the most economical way to heat the
wire would be to take it to the furnace. Yet all electric cooking is
done by sending electric current through wires embedded in the walls of
the cooking utensils, and it is the most wasteful method of using the
energy stored in coal that has yet been devised.

[Illustration: Fig. 68]

That merely connecting the binding posts _a_ and _b_ (Fig. 67) by a
small piece of wire should throw a load upon the dynamo miles away;
should offer resistance to its motion, and make it require 1.18
horse-power more of energy to keep up its speed of revolution, is,
indeed, uncanny. I will attempt to make it seem more real. At one end
of the lecture table I have a rotary pump _P_ (Fig. 68). The end of
the rubber tube _a_, which leads to the pump is lying upon the table
outside of the tank of water, _T_. While things are in this condition
I move the crank which operates the pump with perfect ease. Now while
still turning the crank I pick up the tube _a_ and drop its free end
into the water tank. I cannot now conceal the fact, even if I were
disposed to do so, that I must work hard to keep the pump going. The
pump itself tells you by its laboured sound that it is working hard,
and the stream of water which issues from the pipe _b_ tells how much
work I am performing. The pump is discharging five and a half pints of
water per second, that is 5.5 pounds, and it raises this water 10 feet.
Hence I am doing 55 foot pounds of work per second, which requires
one tenth of a horse-power. Here is a lad who consents to try the
experiment for us. He turns the crank easily while I am holding the
tube _a_ out of the water, but when I lower it into the water he finds
the resistance so great that, tug however much he may, he is unable to
keep the pump going.

At the other end of the table I have a small hand dynamo, _D_ (Fig.
68), _M_ is an ammeter, _V_ is a volt meter, _S_ is a switch. All the
wires are good-sized copper, and offer little resistance, except that
stretched between the binding posts _a_ and _b_. This is a piece of
fine German silver wire. While the switch is open I turn the crank
of the dynamo with perfect ease. A small amount of current is going
through the volt meter, but this is too slight to offer any perceptible
resistance to the motion of the machine.

Notice that the volt meter needle moves according to the speed of
revolution. If I turn the crank once a second the needle stands at
25 volts. The electric pressure increases or decreases according to
whether I rotate the armature faster or slower. Now I will attempt
to keep the machine revolving at a constant rate while I close the
switch _S_, and surely you must see that I have hard work to do so. The
wire _a b_ has now become red hot. The volt meter shows 25 volts of
pressure, and the ammeter shows 3 amperes of current.

Twenty-five volts × 3 amperes = 75 watts, which require one tenth of
a horse-power (746 watts = 1 horse-power). The lad now takes my place
at turning the machine and finds it easy when the switch is open, but
I actually overload him by merely closing the switch. Heating the wire
red hot requires more energy than he is able to put forth.

I proposed to the president that my lecture close at this point, and
that each one in the room have a chance to _feel_ the load which was
thrown upon the dynamo each time it was required to heat the wire.
I suggested that each person should get a realizing sense of this
fact, first by doing the work himself, and second by going home and
reflecting upon this hint. When the switch is closed three amperes of
electricity pass around the circuit. This increases the magnetism in
both the field and the armature of the dynamo, and it requires one
tenth of a horse-power more to keep the armature moving within the
field against this magnetic pull.

I further desired to announce that during this hour I had delivered to
them the second key to the Electrical Show which I had promised a few
days ago. The second key is:

Heat (and light) is produced by offering resistance to the flow of the
electric current. The first key is the electro-magnet. These two unlock
all the mysteries of the show.

The president closed the formal exercises with the facetious remark
that I had warned them before the lecture that they must work, so now
each would be expected to take a turn at the cranks of the pump and
dynamo.




VIII

APPLICATIONS OF ELECTRIC HEATING


The programme committee decided that each member of the Science Club
should busy himself looking for _applications of electric heating_ and
should consult me freely about the matter. My telephone was kept busy,
my laboratory was in great demand, and we were all getting a good deal
more education than the school was giving us credit for.

The boys generally came to me in pairs, and each pair having worked up
some illustration of heat produced by electricity reported it to the
club. These were spread by the secretary in due form upon the minutes
of the club and constituted "The Proceedings of the Science Club."

[Illustration: Fig. 69]

1. _The Electric Sad Iron_ (Fig. 69).--Removing three screws the iron
comes apart, revealing a lot of No. 24 German silver wire wound upon a
sheet of mica. This is put between other sheets of mica (Fig. 70) and
tucked away within the body of the iron. German silver offers about
twice the resistance of iron when it is cold, but, at the temperature
of the sad iron when in use, there is not much difference between the
resistance of the two metals. German silver wire, however, does not
rust as iron wire would, and hence it is chosen. German silver is an
alloy of copper, zinc, and nickel.

[Illustration: Fig. 70]

We put the 112-volt current upon this wire of the iron, and according
to the ammeter it passed 4 amperes. Its resistance must therefore have
been 28 ohms.

    (112 volts)/(28 ohms) = 4 amperes

Electricity costs us about 10 cents per kilowatt hour. That is 10
cents for 1000 watts for an hour, or 1 cent for a hundred watts for an
hour, or, on a 100-volt current, 1 cent for an ampere for an hour. It,
therefore, costs about 4 cents or, more accurately, 4-1/2 cents an hour
to heat this iron.

Persons sometimes carry electric irons with them, when they travel, to
iron pocket handkerchiefs and other small articles while stopping at
a hotel. Before connecting an iron in a chandelier one must know the
voltage used in the building. If the voltage in use in the building is
not the same as that stamped upon the iron, it is not safe to connect
it. Not knowing this, many persons have had the embarrassment of
"blowing a fuse" and extinguishing their own lights, and perhaps those
of others in the same building, and very likely also ruining the iron.

Suppose we take for example this iron stamped _110 V; 400 Watts_. (A
slight variation of 5 or 10 volts will not injure an iron.) The wire in
this iron we found to offer about 28 ohms resistance when hot, and it
lets pass 4 amperes. This is about all the current which it is able to
carry without melting. Now suppose a 220-volt current is used in the
building where it is proposed to connect the iron. This would force
through the wire enough current to melt it. The wire was seen to be
at a very dull-red heat when examined in a dark room. Its temperature
was about nine hundred degrees. At this temperature its resistance is
about three times what it is when cold. We estimated by measurements
that the iron contained about twenty-five feet of the wire. The boys
then took twenty-five feet of No. 24 German silver wire and stretched
it between two nails driven up in the laboratory (Fig. 71, _a b_). The
dynamo current was then sent through this. The end, _c_, of the wire
from the dynamo was provided with a metal clip which could be slid
along on the German silver wire. Sliding this to the left, and thus
shortening the distance on the German silver wire through which the
current must pass, increased the amount of current and heated the wire
hotter. The resistance decreases as the wire is shortened.

[Illustration: Fig. 71]

The boys wound this wire upon a piece of asbestos board (Fig. 72),
about nine inches square and one eighth of an inch thick, taking
care to keep the successive turns half an inch apart. Asbestos paper
was wrapped around this. The two ends of the wire were left free for
connections. This they called a "hot plate."

[Illustration: Fig. 72]

2. _Electric Hot Plate_ (Fig. 73).--This when opened was found to have
wire coiled up inside in the same manner as the sad iron. Indeed the
sad iron supported bottom side up makes a perfectly good hot plate.
The particular hot plate which we examined had a three-point switch
which gave three different heats for the plate. (See Fig. 74.) When the
switch _S_ is upon the first point the current goes through 112 ohms of
resistance and 1 ampere passes:

    (112 volts)/(112 ohms) = 1 ampere

[Illustration: Fig. 73]

[Illustration: Fig. 74]

This warms the plate slightly--enough to keep food warm which has been
already cooked. This costs about one cent an hour.

When the switch is placed upon the second point the current goes
through 56 ohms of resistance and 2 amperes pass.

    (112 volts)/(56 ohms) = 2 amperes.

This makes the plate warmer and is adapted to certain cooking
processes. It costs about two cents an hour.

When the switch is placed upon the third point the current goes through
28 ohms of resistance and 4 amperes pass.

    (112 volts)/(28 ohms) = 4 amperes.

[Illustration: Fig. 75]

We placed upon this hot plate a basin containing 1 pint of water
(equals 1 pound) and heated it from the temperature of the room (68
degrees) to boiling (212 degrees) in 7 minutes and then put an egg in
and boiled it 3 minutes. Using 4 amperes for 10 minutes cost two thirds
of a cent. If it takes 7 minutes to boil a pint of water it would
require 1 hour to boil a gallon upon this hot plate using 4 amperes, or
448 watts. That is, it costs us about 4.5 cents a gallon to boil water
by electricity. The cost is usually put at three and a half cents per
gallon, but much depends upon conditions.

3. _Traveller's Cooker_ (Fig. 75).--This consists of a hot plate with a
covered basin permanently attached to it.

4. _Electric Coffee Percolator_ (Fig. 76) consists of a hot plate
with a coffee percolator to sit upon it. The coffee percolator might
sit upon any other hot plate or this hot plate might serve any other
purpose, but people do not seem to think of that.

[Illustration: Fig. 76]

5. _Electric Chafing-Dish_ (Fig. 77) consists merely of an electric hot
plate with a chafing-dish attached. The electric coffee percolators and
chafing dishes require from 300 to 600 watts according to size. If used
on the 110-volt current they take about 3 to 6 amperes, and if adapted
to the 220-volt current they take from 1-1/2 to 3 amperes, but cost the
same to operate in either case. They have connected with them flexible
cords and plugs to screw into the lamp sockets.

[Illustration: Fig. 77]

6. _Electric Broilers_ are merely hot plates, generally corrugated to
conduct off the melted fat. One that we examined had a switch for three
heats: low, requiring 360 watts--costs 3.6 cents per hour; medium,
requiring 600 watts--cost 6 cents per hour; high, requiring 1280
watts--cost 12.8 cents per hour.

7. _Electric Oven._--This one has double walls to retain the heat and
has two large hot plates, one on the bottom and one on the top. It is
large enough to hold four loaves of bread. It required 1520 watts for
40 minutes to heat it to the baking temperature and one hour to bake
the bread. Hence the cost of the electricity is about 25 cents, about
what the bread would cost in the market.

8. _Electric Incubator._--This is simply a well-ventilated oven warmed
by an electric hot plate and automatically controlled so that it keeps
a constant temperature of 103 degrees. Under these conditions chickens
hatch from hens' eggs in three weeks. An incubator for 5 dozen eggs was
found to take 25 cents' worth of electricity for the whole process of
incubation.

9. _Electric Toaster._--The wire coiled up in sad irons and hot plates
becomes hot enough to scorch cloth and paper, and even set fire to them
if they come in direct contact. We proved this by opening the iron and
touching paper to the wire while it was carrying the current. We also
lighted a cigar by touching it to the wire. Electric toasters have the
hot German silver wire simply covered by a screen.

10. _Electric Cigar Lighters_ (Fig. 78).--The one we examined hung by
a flexible cord from the chandelier. It had a small disk on the side
which contained a lot of fine wire covered by perforated mica. The wire
became red hot when the push button in the handle was pressed. It took
half an ampere of 110-volt current, and operated only while the button
was pushed. As near as we could calculate it cost .0003 of a cent to
light a cigar.

[Illustration: Fig. 78]

[Illustration: Fig. 79]

11. _Electric Curling Iron_ (Fig. 79).--One who has flat hair needs no
curling iron, but those who have round hair may curl it temporarily, if
they will unscrew an electric light bulb and screw into its socket the
plug of an electric curling iron. The flexible cord contains two wires
insulated from each other. One of these wires is attached to the outer
shell of the plug, the other wire is attached to the central button of
the plug. These make connections with the two separate dynamo wires in
the socket. The current comes down one of the wires in the flexible
cord, passes through a coil of fine German silver wire inside of the
curling iron, and returns by the other wire in the flexible cord. The
small wire in the curling iron offers 220 ohms of resistance when hot
and passes half an ampere of the 110-volt current.

    (110 volts)/(220 ohms) = .5 ampere.

12. _Electric Soldering Irons_ (Fig. 80).--Or coppers, as they should
be called, are ideal implements for soldering. They remain continually
at the proper temperature and are free from corrosion. They require
from 55 to 220 watts. On the 110-volt current they take from one half
to two amperes.

[Illustration: Fig. 80]

13. _Electric Heating Pad_ (Fig. 81).--This consists of resistance
wire inside of a pad of soft material. It maintains a temperature of
180 degrees, and is an excellent substitute for a hot water bag. It
contains about two hundred and twenty ohms of resistance and requires
the same current as a 16-candle-power lamp.

[Illustration: Fig. 81]

14. _Electric Fuses_ (Fig. 82).--Fuses are made of short pieces of wire
or thin sheet metal. The metal is an alloy of lead and tin which melts
at a low temperature. They derive their name from the fact that they
readily fuse or melt. A building is wired in various separate circuits.
The size of the copper wires used in each circuit is determined by the
amount of current which the circuit is expected to carry. Each circuit
is protected by one or more fuses. These melt and cut off the current
whenever too much passes for the copper conductor to carry without
getting hot. The fuse wire melts at about six hundred degrees, while
the copper will not melt until it reaches nearly two thousand degrees.
This temperature is sufficient to set fire to wood, paper, and cloth.
When any fuse melts, the current is cut off from all chandeliers,
etc., in the particular circuit controlled by the fuse. This produces
consternation among people who do not understand the function of a
fuse. They become panic-stricken and begin to trample their neighbours
to death in the theatre or on the electric train when they hear that a
fuse is "blown" (which is the electrician's way of saying that it has
melted). Everyone should know that a fuse is a safety device. It is
always enclosed in a box lined with sheet iron or asbestos, so that it
is impossible for the flash, which occurs when the circuit is broken,
to set fire to anything.

[Illustration: Fig. 82]

[Illustration: Fig. 83]

15. _Electric Gas Lighter_ (Fig. 83).--These usually have two or three
small, dry battery cells in the handle. By pushing a button in the
handle connection is made between this battery and a short piece of
resistance wire in the tip. This wire gets red hot and lights the gas.
It is a surprise to many that we can light illuminating gas without
bringing a flame to it, and it is equally surprising that some flames,
or at least sparks, may not be able to light the gas. The fact is that
it is wholly a matter of _temperature and kind of gas_. Iron heated to
dull red will not light the illuminating gas now being furnished in
New York City, while iron at a bright red heat will do so. Iron may be
hot enough to light illuminating gas but too cool to light gasolene
vapour, which requires a dazzling white heat. Iron which is just under
the temperature at which it gives any light may set fire to wood and
paper. After it has cooled a good deal below that, it will set fire to
sulphur, and when it has cooled so that one may hold it in the hand,
it is still hot enough to set fire to phosphorus. The glowing end of
a lighted cigar, the spark made by striking flint, or the spark from
a spark coil with a feeble battery, all fail to set fire to gasolene
vapour, simply because they are not hot enough.

Fresh battery cells must occasionally be put in the handle of the
electric gas lighter.

Four facts regarding the resistance of wires it is well to remember:

1. The longer the wire the more resistance it offers to the electric
current.

2. The smaller the diameter of the wire the more resistance it offers.

3. Some materials offer more resistance than others, for example, iron
about six times as much as copper and German silver about twelve times
as much as copper.

4. The common metals offer more resistance when hot than when cold,
about double the resistance when heated to five hundred degrees. It is
the reverse with carbon, which offers more resistance when cold than
when hot. The carbon filament lamp offers about double the resistance
when cold as when lighted to full brilliancy.

16. _Electric Flasher_ (Fig. 84).--For automatically flashing electric
lights. The one which we examined was constructed according to the
plan shown in Fig. 85. The lighting circuit is brought to the binding
posts _b_ and _c_. A small insulated wire of high resistance connects
_b_ and _c_, being wound around the metal bar _a b_. The resistance of
this wire, when added to that of lamps, permits not more than one fifth
of an ampere to pass, and this warms the wire slightly. The bar _a b_
is composed of two strips of metal, brass above and iron below. Heat
expands brass more than iron. The result is that when the current is
turned on, the bar begins to curve downward until presently it touches
the metal base of _c_. Then the full current required to light the
lamps which are in circuit passes. While the circuit is closed through
the large metal strips not enough passes through the fine wire to warm
it. On cooling, _a b_ curves upward and breaks the connection with _c_,
and now the current begins again to warm up the small wire.

[Illustration: Fig. 84]

[Illustration: Fig. 85]

The flasher that we examined was adapted to operate: one
32-candle-power lamp; or two 16-candle-power lamps; or four
8-candle-power lamps, on a one ampere circuit of 110-volt pressure.

Let us see what would happen if it were connected either with a
current of higher voltage or a circuit of more lamps. Suppose we have
a 32-candle-power carbon filament lamp in circuit. This requires one
ampere to light it. Its resistance when hot is 110 ohms.

    (110 volts)/(110 ohms) = 1 ampere.

When cold its resistance is about double or 220 ohms. The German
silver wire of the electric flasher offers 330 ohms of resistance, and
together they make 550 ohms. Thus the current is cut down to .2 ampere.

    (110 volts)/(330 + 220 ohms) = .2 ampere

Suppose now we should undertake to use the same flasher and the same
lamp on a 220-volt current. This might push more current through than
the small wire could carry. It might melt, or its insulation might burn
off before _a_ made contact with _b_; if not the lamp would certainly
burn out after the contact. If we undertook to operate with this
flasher several 32-candle-power lamps instead of one upon the 110-volt
circuit, the result would be the same, for in that case the resistance
would be reduced and, therefore, a greater current would pass than the
wire could carry without undue heating.

[Illustration: Fig. 86]

The boys were at first troubled to see how increasing the number of
lamps in a circuit would decrease the resistance in that circuit. Fig.
86 was drawn to explain the matter. The lamps _l_, _l_, _l_, etc., are
connected _in parallel_. Each lamp makes an independent connection from
one feed wire to the other. The flasher _a_ acts as a switch to close
the circuit for the whole.

Now if we think of these wires as pipes to conduct water we would say
that water flows from _D_ to _E_ through ten pipes more readily than
through one. It would meet with only one tenth as much resistance. The
result would be the same, if we should substitute for the ten pipes one
pipe ten times as large in cross section. So it is with wires which are
conducting electricity. Introduce two in parallel, and you allow twice
as much current to pass by reducing the resistance to one half. Ten
parallel conductors reduce the resistance to one tenth and allow ten
times as much current to pass.

[Illustration: Fig. 87]

It is to be noticed that this flasher is an automatic switch which is
opened or closed according to temperature. Remove the fine wire from
_a_ and we have precisely the device which regulated the temperature in
our electric incubator. Suppose the "thermostat" (as it is called in
that case) is placed within the egg chamber which is to be kept at 103
degrees. A screw in the metal strip _c_ underneath the end of _a_ may
be set so that it will normally touch _a_. Suppose now the brass strip
is underneath the strip of iron in _a_. As the hot plate warms up the
egg chamber, the brass will expand more than the iron, and the bar will
curve upward and break the connection with _c_. As soon as the current
stops the temperature of the chamber begins to fall, and the bar curves
downward again until connection is made. This device is capable of
adjustment so as to keep the temperature constantly at 103 degrees or
any other desired degree. The device is in use for scores of different
purposes, including the regulation of temperature in school rooms.

17. _Electric Car Heaters._--Ten or fifteen years ago there were
no heated street cars in New York City. Now they are all heated by
electricity and their maximum and minimum temperatures are regulated by
law. The resistance wire may be seen in coils underneath the car seats.
Electric street cars usually operate on a 500 or 600-volt current. The
amount of current used for heating varies from 2 to 12 amperes. Perhaps
3 amperes may be taken as an average.

    500 V × 3 _a_ = 1500 _w_ = 1-1/2 kilowatts.

It costs the large electric railway companies about 1.5 cents per
kilowatt hour to generate their supply of current. Eighteen hours is
considered a car day.

    1-1/2 kilowatts × 18 hours = 27 kilowatt hours.

    27 kilowatt hours at 1.5 cents = 40 cents per car day.

18. _Heating Apartments by Electricity._--For heating apartments
by electricity the same sort of apparatus is used as that already
described for heating cars. A family of four adults, living in an
eight-room apartment with at least 120 cubic feet of fresh air
admitted per minute, will use on an average ten amperes of the 110-volt
current. The cost will be about two dollars and fifty cents per day
or seventy-five dollars per month. Although this is as much as the
entire rental of a perfectly comfortable apartment, the novelty and the
convenience attract tenants and the extra cost of rent does not deter
them.

[Illustration: Fig. 88]

19. _Electric Bedroom Heater._--One of the boys constructed a heater
for his own room as follows: He procured a box eight inches deep by
eighteen inches square on the bottom. This he lined with asbestos
paper. He then stood it upon its side and arranged four incandescent
light sockets as shown in Fig. 88. These were connected by a flexible
cord to a plug which he could insert in place of a lamp in the
chandelier. He placed this heater on the floor underneath the window
and usually had 16-candle-power lamps in the sockets. He claimed that
it was a jolly foot warmer and kept the room comfortable without other
heat. He turned on from one to four lamps according to his need and
replaced the 16-candle-power lamps by 32-candle-power lamps when
the weather was extremely cold. I remarked that he must have light
along with heat by this arrangement, and I should think that might be
objectionable when he desired to sleep at night. He said that he always
turned it off, and opened the window at night, always preferring a cold
room to sleep in.

[Illustration: Fig. 89]

20. _Cooking with Incandescent Lamps._--This piece of apparatus was
devised by the boys and used in my laboratory. A sheet iron basin _a_,
was inverted over four 16-candle-power incandescent lamps, shown in
elevation by Fig. 89, and shown in plan by Fig. 90. The sides of the
basin were cut so as to admit the glass globes of the lamps, but the
sockets and keys were outside, so that it was convenient to turn on
and off the lamps separately, thus using one half to two amperes of
current, as desired. This rested upon another basin, _b_. Basin _b_
was covered with asbestos for the lamps to lie on and the whole was
attached to a board base, _c_. A flexible cord and plug allowed us to
attach this to the chandelier. A pint of water was boiled upon this
stove in fifteen minutes, and refreshments have been served hot from it
repeatedly.

[Illustration: Fig. 90]

21. _Electric Fireless Cooker._--There are five indictments against
ordinary cooking processes.

1. They heat the house in summer.

2. They convert what would be pleasant flavours in the food into
noxious odours about the house.

3. They cannot be controlled with regard to time and temperature as
scientific experiments should be.

4. They confine the cook too closely and are not sufficiently automatic.

5. They are wasteful of fuel.

It would seem that electricity might enable us to cure most of these
evils. To be sure the production of heat by electricity is wasteful
of fuel, and it seems doubtful how the account will balance regarding
the fifth item. But the remaining four items furnish a very hopeful
field for research. I use the last word advisedly, and think it is just
as applicable to high school boys as to university students. After
experimenting awhile the boys and I concluded to give a dinner party
in the laboratory and invite a few friends to test the results of our
cooking.

We procured a cylinder of magnesia such as is used for covering large
steam-pipes. This was inverted over our electric stove which was
illustrated in Fig. 89. The magnesia was cut at the bottom, so as to
give access to the key sockets of the lamps, (Fig. 91). First upon the
electric stove was placed a covered dish containing a roast of lamb.
Above this was another dish containing a vegetable, and upon the top of
that was a pudding. A flat piece of magnesia was used as a cover to the
whole. Through a hole in this was suspended a thermometer.

[Illustration: Fig. 91]

This "fireless cooker" was sitting in the centre of the dinner
table when the guests gathered around it. We had these problems for
investigation:

1. Will this cooker heat the house in summer?

All testified that they did not know that there was any heat about it
until they laid their hands upon it, and then they found it only very
slightly warm.

2. Is there any smell of cooking here? The process has been carried on
from start to finish right on this table.

All agreed that no smell could be detected.

I then turned off the electric current which had been running until now
and served the meat and vegetable, leaving the pudding inside to be
kept warm by the hot walls of the cooker.

3. Regarding the control of the process: we were using 32-candle-power
lamps, which gave us a variable current, from 0 to 4 amperes, and a
watch and a thermometer. We had control, but as yet lacked knowledge of
how it should be used. In the present case we had arbitrarily decided
to begin with temperature of 400 degrees, continue it for 20 minutes,
then turn off all the electric current, and let the temperature fall
gradually. This had been done at our convenience in the morning before
school. At a quarter before twelve we had found the temperature at
200 degrees, and turned on all the current, and now, at five minutes
past twelve o'clock, all testified that the lamb was particularly
good--neither too well done nor undercooked, and that its flavour was
better than usual.

As for economy of fuel, we find at least that we get better results
from incandescent lamps than from hot plates used in the same
apparatus, and the electric equipment enables us to put the heat
exactly where it is needed and nowhere else.

22. _Incandescent Lamp._--We feel quite justified in putting the
incandescent lamp under the heading, _Applications of Electric
Heating_, since the electric lamps in general use convert 96 per cent.
of the electric energy into heat and only 4 per cent. into light.

They were originally made by introducing a short piece of fine wire
into the circuit, choosing the kind of wire, its diameter, and its
length so as to make the proper relation between resistance and
voltage, in order that enough current might pass to make it white hot,
but not quite melt it. Platinum wire was first chosen because it would
stand the highest heat without melting and without rusting.

We will pass our 112-volt current through 9 feet of the No. 24 iron
wire. The wire is heated to bright red, but does not melt as it did
when we used 8 feet in a former experiment. The increased length has
added resistance, and, as you see by the ammeter, cut the current down
from 8 to 7.5 amperes. I will now darken the room and you find that
it is giving light enough to read by. But you notice that the light
is growing dimmer, its colour is growing redder, and the ammeter
indicates that less current is passing. I will cut off the current
and let you examine the wire and you notice that a crust has formed
upon it. This is due to the oxygen of the air which unites with the
iron, forming iron rust. Iron rust does not conduct electricity. We
have converted No. 24 iron wire into a wire of smaller diameter with a
sheath of iron rust around it. We might prevent the rusting by putting
the wire in a glass globe and exhausting the air from it.

I have here a piece of No. 24 platinum wire which has about the same
resistance as iron wire when cold, but you notice that I may use a
very much shorter length than I did of the iron wire because it will
endure a very much higher heat without melting. Reducing the length
would reduce the resistance, but reducing the resistance would allow
more current to pass. If more current should pass it would make the
wire hotter, and raising the temperature would increase the resistance,
which would cut down the current, etc. By sliding the clip _c_ (Fig.
92), along, I finally reach a point where conditions balance so that I
get a very brilliant light, dangerously near the fusing point of the
platinum which is three thousand degrees above the boiling point of
water.

In 1879 Mr. Thomas A. Edison literally searched the whole world for
something better than platinum for the filament of an incandescent
lamp. He finally decided upon charred threads of a bamboo which he
found in Japan. No research was ever more timely than this. Whereas
there was practically no electric lighting before 1880, soon after
that there began a phenomenal demand for carbon filament lamps. In
1890, 800,000 of these lamps were manufactured in the United States. In
1900 the number had risen to 25,000,000. In 1909 central stations were
supplying electric current to 41,807,944 incandescent electric lights.
By far the greatest number are still made with carbon filaments.

[Illustration: Fig. 92]

[Illustration: Fig. 93]

We examined an ordinary 110-volt 16-candle-power carbon filament lamp,
(Fig. 93). As near as we could estimate, its filament measured about
eight inches in length. We broke open the bulb of this lamp by laying
it upon the table and tapping it with a board. The bulb broke with
rather a loud noise and the brittle carbon filament broke into many
pieces. We found one of these pieces and measured its diameter with a
wire gauge, (Fig. 94). It was the same size as No. 33 wire, which we
also found by the wire gauge was the size of No. 90 sewing cotton. The
diameter of No. 33 wire was given upon the wire gauge as .007 inch.
When lighted, the filament of this lamp had looked to be about the size
of No. 18 wire, which has a diameter of .04. That is, the filament
when lighted looked six times as thick as it really was. Those who
use sewing cotton learn quickly to know the size of the thread by its
number. So those who have much to do with wire easily learn the system
of designating sizes by numbers. Here are some selected figures easy
to remember. A trolley wire is about one third of an inch in diameter.
It is designated as No. 0. Notice in the following table that as the
numbers rise by six the diameters are divided by two. Notice also that
as the diameters diminish by two the resistance increases by four.

[Illustration: Fig. 94]

       TABLE OF RESISTANCE OF COPPER WIRES

    _Nos._    _Diameter_             _Resistance_

     0      .32 inch      10560 feet to the ohm
     6      .16   "        2640   "   "  "   "
    12      .08   "         660   "   "  "   "
    18      .04   "         165   "   "  "   "
    24      .02   "          40   "   "  "   "
    30      .01   "          10   "   "  "   "
    36      .005  "           2.5 "   "  "   "
    42      .003  "           1   "   "  "   "

    10,560 feet equal two miles.

Number 36 is the wire used upon the spools of telegraph receivers. They
offer 75 ohms of resistance and therefore contain 30 feet of wire (30 ×
2.5 = 75). These resistances are for ordinary school room temperatures.

Since iron has six times, and German silver twelve times the resistance
of copper, divide the figures of the third column by six, and the table
will answer for iron wire, or divide those figures by twelve and the
table may be used for German silver wire, thus:

                              _Number Feet to the Ohm_
    _Nos._ _Diameter_    _Copper_    _Iron_   _German Silver_

     0     .32  inch      10560       1760        880
     6     .16    "        2640        440        220
    12     .08    "         660        110         55
    18     .04    "         165         27         14
    24     .02    "          40          6         32 inch
    30     .01    "          10          1.5        8  "
    36     .005   "           2.5         .45       2  "
    42     .003   "           1          2 inch     1  "

These figures are not exact, but useful.

We procured a string of eight small lamps (Fig. 95), such as are used
in lighting Christmas trees. Each was marked 14 volt, 2-candle-power.
The carbon filament of each was about one inch long and apparently the
same diameter as that of the 16-candle-power lamp. When the 110-volt
current was sent through the group of eight connected in series they
seemed to give about the same light as the single 16-candle-power lamp.
It is as though the filament of the 16-candle-power lamp had been
cut into eight pieces, and distributed through eight small lamps. We
introduced an ammeter into the circuit and found that half an ampere of
electricity passed through the single 16-candle-power lamp--and half an
ampere likewise passed through the group of eight 2-candle-power lamps.

[Illustration: Fig. 95]

The 110-volt current can push an ampere of electricity through eight
inches of carbon thread seven thousandths of an inch in diameter, and
when this happens the filament gets hot enough to give out as much
light as sixteen standard candles. In the place of the 16-candle-power
lamp, we put a 32-candle-power 110-volt lamp. The ammeter indicated
one ampere. The carbon filament was larger (No. 30, diameter =
.01 inch), so as to allow more current to pass. An 8-candle-power
110-volt lamp was substituted; one quarter of an ampere passed. A
4-candle-power 110-volt lamp was used; one eighth of an ampere passed.
A 100-candle-power 110-volt lamp was substituted; three amperes of
current passed through it. In all these cases the lamps which passed
the larger current had the larger filaments. A little practice would
enable one to distinguish between these lamps without labels by
examining their filaments. Among these 110-volt lamps, it is to be
noted that the amount of light which they give is proportional to the
amount of current which they pass. And it is convenient to remember
that one ampere of electricity for one hour costs about one cent.

We introduced into the socket a "Hylo" lamp (Fig. 96). The filament,
_A_, took half an ampere of electricity, gave 16-candle-power of
light, and cost half a cent an hour. When the lamp was turned in its
socket the current was switched off of the filament _A_, and on to the
filament _a_. This took .03 of an ampere, gave one candle-power of
light, and cost .03 of a cent an hour, or at the rate of about $3.00 a
year, burning continuously day and night.

[Illustration: Fig. 96]

The uses of such a lamp are apparent in rooms which have no daylight.
However, a wall switch at the entrance of such a room, making it easy
to throw on and off the light entirely, seems to be a more satisfactory
arrangement. One of the boys connected a wattmeter in the circuit with
a hylo lamp and found that the small filament did not pass current
enough to move the armature of the wattmeter. Hence that may be burned
alone without affecting the consumer's bills.

We took a 16-candle-power 220-volt lamp, and lighted it by a 220-volt
current. The meter showed that it allowed only one quarter of an ampere
to pass. The filament was very much smaller than that in the 110-volt,
16-candle-power lamp. The pressure was twice as great as before, but
the resistance was four times as great, and hence only half as much
current passed. We find that it costs just as much to generate one
quarter of an ampere at 220-volt pressure as it does to generate half
an ampere at 110-volt pressure.

We must, of course, pay for electricity according to the cost of
producing it. To produce .5 ampere at 110-volt pressure costs the same
as one ampere at 55-volt pressure, or .25 amperes at 220 volts. It will
be noticed that the products of the two factors in each case are the
same. The product of an ampere multiplied by a volt is a watt. In each
of the above three cases the amount of electrical energy is 55 watts.
This will produce a definite quantity of light--about 16 candle-power
when the carbon filament is used, and this quantity does not vary as
either volts or amperes, but as the product of these, namely, watts.

Each of these lamps is called a 55-watt lamp, and, since they each give
16 candle-power of light, a carbon filament lamp gives one candle-power
of light for three and a half watts of electricity. Electricity for
lighting purposes usually costs _10 cents per kilowatt hour_, that is,
10 cents for 1000 watts for one hour, or one cent for 100 watts for
one hour. Hence a 55-watt lamp costs a trifle more than half a cent for
one hour, or exactly .55 cents, and a 32-candle-power lamp costs 1.1
cents per hour.

We introduced into the socket a 48-candle-power 110-volt tungsten lamp
(Fig. 97), and turned on the 110-volt current. The ammeter showed
55 ampere. Hence the lamp is a 60-watt lamp, and requires one and a
quarter watts per candle-power. That is, the metal tungsten is nearly
three times as efficient as carbon for producing light from electricity.

[Illustration: Fig. 97]

With pincers we broke off the tip of a 32-candle-power carbon filament
lamp, making a small hole in the large end of the bulb. The air rushed
in. We then put the lamp in the socket and turned on the current.
The carbon filament glowed as usual, and slowly burned up, growing
smaller as it did so. The ammeter which was in circuit showed that the
current, which was one ampere at the beginning, grew steadily less as
the filament grew smaller, until finally when it was about one quarter
of an ampere, the circuit was broken by the filament burning in two.
We removed the lamp from the socket and with a dropper tube introduced
a little lime water, and shook it to absorb any gas which might have
been formed in there. It became milky white, as it always does when
introduced where carbon has been burned. This would be a sufficient
proof that the filament was made of carbon, if we did not already
know it. The air is exhausted from these bulbs to prevent the carbon
filament from burning up.

[Illustration: Fig. 98]

The carbon filament lamps were, as has been said, the invention of
Mr. Thomas A. Edison in 1879. Such a statement must, however, be
qualified by the assertion that this, like nearly all invention, was
but the consummation of a long line of researches made by many men for
many years. The early filaments were made of bamboo thread, charred,
but now they are drawn like spider's web out of a sticky liquid and
carbonized at a high temperature. They are attached in the lamp to
short pieces of platinum wire which are sealed through the glass walls
of the bulb. One wire connects with the brass collar of the bulb, and
the other with the central piece of brass at the base of the bulb.
We dissected a socket and found that when the lamp is placed in the
socket, the collar of the lamp is screwed into the collar of the
socket, and the base of the lamp comes in contact with a brass spring
in the bottom of the socket (Fig. 98). The spring is connected with
one copper wire bringing electricity from the dynamo. The collar is
connected with the other wire from the dynamo. This connection is made
and broken by turning the key of the socket. The wires are made of
copper since copper is a particularly good conductor of electricity.
No electricity can flow unless this circuit is complete. Socket keys
and wall switches make or close gaps in this circuit. No copper wires
for carrying electric-lighting current are smaller than No. 12, which
has a diameter of .08 or about one twelfth of an inch. The intention is
to have as little resistance to the current as possible, except in the
filament of the lamp itself. There resistance is purposely introduced
in order to convert electricity into light, light without heat if that
were possible, but since that has not yet been found possible, heat for
the sake of the accompanying light. Unhappily only 4 per cent. of the
electrical energy goes into light and 96 per cent. goes into useless,
or even harmful, heat. The tungsten lamps, which are now coming into
use, are nearly three times as efficient in the production of light as
are the carbon filament lamps. The dynamo exerts its entire pressure
upon the lamp and furnishes current as follows:

A dynamo of 110-volt pressure gives:

1 ampere = 110 watts, through a 32-candle-power lamp, cost one cent an
hour, or

.5 ampere = 55 watts, through a 16-candle-power lamp, cost half a cent
an hour, or

.25 ampere = 27-1/2 watts, through an 8-candle-power lamp, cost a
quarter of a cent an hour.

A dynamo of 220-volt pressure gives:

.5 ampere = 110 watts, through a 32-candle-power lamp, cost one cent an
hour, or

.25 ampere = 55 watts, through a 16-candle-power lamp, cost half a cent
an hour, or

.125 ampere = 27-1/2 watts, through an 8-candle-power lamp, cost a
quarter of a cent an hour.

The carbon filament lamps, barring accidents, have a natural life
varying from 600 to 1000 hours of actual incandescence. At the end of
that period the filament has become so thin that it will fall apart by
ordinary usage. It is never profitable, however, to use them for their
whole lifetime. The lamp gradually volatilizes carbon and deposits
it upon the inner walls of the bulb, producing a smoky appearance and
shutting off light. As the filament grows thinner by this process, it
offers greater resistance to the current, and as the amount of current
grows less the proportion of light to current grows rapidly less,
so that at last instead of paying for 3.5 watts of electricity per
candle-power of light one must pay for perhaps seven or eight watts per
candle-power. We pay fifteen cents apiece for 16-candle-power lamps,
and it is economy to renew them about twice a year, if they are burned,
say three hours a day, or a little over five hundred hours. It is
interesting to note that when a direct current is used the evaporation
from the carbon filament always takes place at the negative end alone,
that is, the end from which the current is leaving the lamp. If an
alternating current is used the evaporation goes on from all parts of
the filament alike. This is a case of evaporation from the solid state.
Carbon does not boil below 6,000 degrees, and the filament reaches
about 2,450 degrees.

Tantalum, tungsten, and osmium lamps have metal filaments. These metals
are better conductors than carbon but unlike carbon their resistance
increases as their temperature rises, and their special virtue is that
they are capable of enduring an extremely high temperature without
melting. The wire used in some of these filaments is as small as .002
of an inch, or No. 44. In order to furnish sufficient resistance to
prevent the 110-volt current from melting, they often have a length
exceeding two feet. This is laced back and forth within the small bulb.
At the temperature of bright incandescence their resistance may be
increased as much as fivefold and sometimes becomes about ten ohms to
the inch. Like all metals they are more brittle when cold than hot.
Hence when cleaning such lamps it is advisable to turn on the current
to avoid breaking the filament by jarring. Filaments which are too
fragile to endure the jar of ordinary railway travel, when cold, have
gone through railway wrecks safely when lighted.

It is a general rule that good conductors of electricity grow more
resistant as the temperature rises while non-conductors resist less as
the temperature rises. Hence the insulating material which is used to
cover copper wires fails to protect if highly heated.

If a 110-volt lamp is put into a 220-volt circuit, one might expect
that the lamp would burn out without doing further damage to the
circuit, but this is not the case. As the filament approaches its
melting point, 6000 degrees, it becomes so good a conductor that it
carries current enough to melt a fifteen ampere fuse. It is, therefore,
the fuse that protects the circuit and not the burning out of the lamp.
The bulb containing the highly heated carbon vapour would conduct the
current as an arc lamp does.

[Illustration: Fig. 99]

23. _Arc Lamp._--We fastened two electric light carbons to the ends of
copper wires connected for the 110-volt current. A rheostat, _R_ (Fig.
99), in circuit, was set at 6.5 ohms. One lower carbon was fastened
into a clamp, and the other was touched to it, and then drawn away
about three-eighths of an inch. A very brilliant light was produced.
Probably about 1800 candle-power. The ammeter _A_ showed 10 amperes,
and the volt meter _V_ showed 45 volts. 45 volts × 10 amperes = 450
watts, 1800 candle-power, 25 watts per candle-power.

The arc light is the cheapest of all lights but is too dazzlingly
bright for household purposes. It is used for outdoor lighting
chiefly, and particularly for large search-lights. The temperature is
over 6000 degrees, which boils the carbon and fills the gap between the
two pencils with a stream of carbon vapour. This conducts the current
like the filament in an incandescent lamp. The air gap between the
carbon pencils would have a resistance of many thousand ohms if it
were not for the presence of the carbon vapour. The hot carbon vapour
reduces the resistance of this space to 4.5 ohms.

    (45 volts)/(4.5 ohms) = 10 amperes.

or

    (110 volts)/(6.5 + 4.5 ohms) = 10 amperes.

The carbon pencils account for part of this resistance--not more than a
third of an ohm however.

It is evident that arc lamps in use must have an automatic mechanism
which shall permit the carbons to touch whenever the current is not
passing, but which shall draw them apart to the proper distance after
the carbon vapour has been formed, or, as we say, after the arc has
been established. This mechanism is nothing else than electro-magnets
which are operated by the lighting circuit itself. It may require
thoughtful examination to recognize these as electro-magnets, in every
case, but that is what they are. Sometimes they are coils of wire,
which do not have iron cores and armatures separate to be sure--but
nevertheless they have both of these united in one movable rod, and
they produce magnetic fields.

Suppose I pass an electric current around this coil _A_ (Fig. 100).
The region about the coil becomes a magnetic field with its north pole
situated at a point in space, say _N_. The influence of this field
causes the iron rod to become a magnet with its south pole uppermost,
and if the current is strong enough, and the field which it produces is
strong enough, it will lift the iron rod up into the coil. By varying
the strength of the current you see I may make this rod dance up and
down in space touching nothing--a veritable ghost dance.

[Illustration: Fig. 100]

It may be pettifogging to say that the upper portion of this iron
rod is the core of the magnetic field, and its lower portion is the
armature. Yet this is right, and pettifogging may be right when it is
the only way to bring out the fact.

Our great study now is to produce light without heat, or at least to
come as near to it as the firefly does. The firefly gives 98 per cent.
light and two per cent. heat. The arc lamp gives 12 per cent. light
and 88 per cent. heat. The carbon filament gives 4 per cent. light and
96 per cent. heat. When we have made considerable progress in that
direction we shall take electric lamps out of the chapter on electric
heating and form a new chapter on electric lighting.

One might expect that a rod made of carbon would quickly burn up,
particularly when raised to the exceeding high temperature of the
electric arc. While it is true that carbon in the form of charcoal
burns so readily that it is used instead of kindlings for lighting a
fire, carbon in the form of graphite in our so-called "lead" pencils
and carbon as it is prepared for electric light pencils burns only very
slowly even at exceedingly high temperatures. The carbon rods used in
arc lamps endure a temperature of over 6000 degrees, without losing
more than one inch an hour, and half of that is simply volatilized--not
burned.

One of the most interesting improvements ever made in the arc light
is that of enclosing the arc in an inner glass globe. This globe
is closed airtight below with a small opening above. When the arc
is formed the oxygen of the air in the inner globe is soon consumed
and then combustion is no longer possible. We illustrated this by
an experiment. An ordinary cork was chosen to fit the large end of
an argand lamp chimney and through a hole in this was passed one of
the carbon rods (Fig. 101). A metal clamp made connections between
this carbon and the negative wire from the dynamo. The other carbon,
attached by a clamp to the positive wire, was thrust down into the
upper end of the chimney until it touched the negative carbon, and then
drawn upward a short distance, drawing an arc, as we say. This soon
makes an atmosphere within the chimney where combustion cannot go on
for want of oxygen. The arc, however, continues to glow as in the open
air, and the carbons may be drawn further apart than in the open air
without breaking the arc, hence more of the external resistance may be
cut out and a higher voltage put upon the lamp.

[Illustration: Fig. 101]

Carbons which burn out in a single night if used in open arc lamps last
two weeks in enclosed arc lamps.

The lower carbon, when removed from the lamp chimney of the last
experiment, served as a lead pencil to write on paper. The positive
carbon would not make a mark on paper. In all arc lamps carbon is
distilled from the positive pencil, condensing upon the negative pencil
as graphite, which is the material used in making "lead" pencils. They
are called "lead" pencils because they were originally made of lead,
but now they are made of graphite which is mined from the earth.

As soon as the arc is broken it becomes evident that the positive
carbon has been heated much the hotter of the two, a fact that could
not be detected while it was lighted because of the dazzling brightness
of the arc. The negative carbon turns black almost immediately, while
the positive carbon remains at a bright red heat for some time.

This fact needs to be borne in mind when adjusting arc light carbons in
search-lights, stereopticons, and all like apparatus in which the light
must be placed at the focus of a lens. That is, it is necessary to know
from what point the light really comes and it is necessary to have some
adjusting device to keep this point continually at the focus of the
lens.

24. _Search-Light._--(Fig. 102). This is simply an arc lamp with
reflectors behind it and lenses in front of it. The whole apparatus is
pivoted so as to be easily made to shine in any direction. The function
of the lenses and the reflectors is to collect stray rays of light and
send them all out in the same direction. This is shown in Fig. 103
where for simplicity the lens is represented as a single piece. _L_
represents a point of light which will naturally send its rays out in
all directions as the radii of a sphere; _m_, _m_, _m_ represents a
bright reflecting surface which is given that peculiar curve called
a parabola. It has the unique faculty of reflecting in a parallel
direction all the rays which may fall upon it from _L_, so long as _L_
is kept at that particular point called the focus, _a b_ is a lens of
glass which has that peculiar curve that enables it to bend all rays
which fall upon it from _L_, so that they may pass out parallel.

[Illustration: Fig. 102]

25. _Stereopticon._--This also has the necessary devices to gather the
rays of the arc lamp and send them forth parallel, and in addition it
has a series of lenses which produce upon a distant screen an enlarged
picture of any transparent object held in these parallel rays.

[Illustration: Fig. 103]

[Illustration: Fig. 104]

26. _Burglar's Flash-Light._--There are many forms of this. The one we
examined is represented in Fig. 104. We unscrewed a metal ring at the
left-hand end and found, first a glass lens and behind that a miniature
electric light, requiring three volts and half an ampere. We knew,
therefore, that it must be supplied with two cells, since one cell
may give not more than 1.5 volts. We also knew that it would only be
used to _flash_ a light, since if dry cells are required to furnish
half an ampere continuously they soon run down. Behind the lamp there
was a bright metal reflector--the lens and reflector are fairly well
represented in Fig. 103. The filament of the lamp is connected with two
small battery cells in the handle. These may be removed and replaced
by new ones by unscrewing a cap at the right-hand end. The circuit is
closed by a metal spring on the side of the tube, which acts as a push
button. It is situated where it may be conveniently pressed by the
thumb. The small batteries necessarily have a short life and must be
replaced quite frequently. Being a special thing they cost nearly twice
what the regular dry cell does.

[Illustration: Fig. 105]

27. _Mercury Vapour Lamp._--This is an interesting variety of arc
light in which the vapour of mercury takes the place of the vapour of
carbon. _G_, in Fig. 105, represents a glass tube from which the air
has been exhausted. The wires of the lighting circuit are fused into
the ends of the tube. At one end, and in contact with one of these
wires, is a small pool of mercury. By pulling the cord _c_ the tube is
tilted on the pivot _p_, so that a stream of mercury flows along the
whole length of the tube and closes the electric circuit. When the tube
falls back into its normal position, as represented in the figure, the
electric arc persists upon the mercury vapour. Incandescent mercury
vapour gives light strong in green, blue, and violet, but deficient in
red and yellow. It, therefore, gives nothing its natural appearance but
casts a ghastly hue over everything.

This lamp was invented in 1902, by Peter Cooper-Hewitt, grandson of the
founder of Cooper Union in New York City.

It gives a very suitable light for making photographic prints, and is
much used for that. This lamp operates upon the 110-volt circuit. It
is the longest step yet taken toward getting light without heat, but
perhaps shows what we must expect when we reach that goal, namely,
unsatisfactory colour values in the light. Probably such is the case
with the firefly.

28. _The Moore Light._--In 1896 Prof. D. McFarland Moore brought out
his vacuum tube light (Fig. 106). We visited an ordinary dry goods
store which had been equipped with this. Glass tubing is put together
very much as one would put up a stove pipe or a job of plumbing. The
joints are fused and made air-tight by playing a flame upon them after
the pipe is up in place. This pipe is led around into all nooks and
corners where there would be dark places. The air is pumped out of
this tube and a trifling amount of some vapour is introduced, the kind
varying according to the tint of colour which is desired.

[Illustration: Fig. 106]

Metal terminals are fused into the ends of this tube. The tube we saw
was seventy-five feet long. A 1000-volt alternating current is applied
to the terminals and the vapour becomes incandescent, filling the whole
tube full of light. The first thing that the boys remarked was that
although the room was brilliantly lighted no object cast a shadow. It
seemed as though light was everywhere and there was no chance to screen
it off.

29. _The Nernst Lamp._--In 1897 the Nernst lamp appeared in Germany. It
is a good illustration of an insulating substance becoming a conductor
when heated to a high temperature. The "glower," as it is called, is
composed of one or several short rods of clay-like material. This is
first heated by sending the electric current through resistance wire
placed directly underneath it and connected in shunt with it. When it
gets hot, current begins to pass through it, and is automatically cut
off from the resistance coil. The glower produces an intensely bright
and white light although it does not itself exceed the temperature of
1742 degrees.

Electric installations are now so carefully constructed that fires from
poor insulation are very rare. Less than one fire in three hundred
appears to be traceable to that cause.

30. _Electric Welding._--Nothing is more common in electrical matters
than heat produced by poor contacts. In this laboratory are two
chandeliers, each controlled by a wall switch. After the current has
been on the chandeliers for half an hour you will always find one of
those wall switches warm, while the other is not perceptibly warmer
than other objects in the room. The explanation is that there is poor
contact in one of them. When two metal conductors touch one another
at a mere point the electric current, in passing from one of these
conductors to the other across such a narrow bridge, meets resistance
and develops heat--sometimes heat enough to fuse the point, and either
break the contact, or, what is more likely, start a minute arc at that
point. In some cases this makes the apparatus dangerously hot, and in
other cases it bridges the gap with a broader and better contact--a
true electric weld. Electric welding is applied to everything, from
chicken fence to railway rails. Enormously large currents are used for
the purpose, in some cases as high as 50,000 amperes being employed.
The rails of railroads are welded end to end by a current of several
thousand amperes sent through the joint by perhaps two or three volts.
The joint heats and fuses together merely because the poor contact
offers resistance to this enormous current.




IX

LIGHTING A SUMMER CAMP BY ELECTRICITY


Summer had arrived. The Science Club had held its last meeting for the
season. Harold had engaged three other boys to spend the summer at the
farm. I had the roof of an old mill reshingled and gave it to them
for a camp. They were to make it over inside. I sent the boys to the
country as early as it was possible for them to get away. It would be
six weeks later before I could follow them.

[Illustration: Fig. 107]

When I did arrive I found they had elaborate schemes indeed. The first
floor of the mill had been partitioned off into rooms, as shown in
diagram (Fig. 107), _a_, _b_, _c_ and _d_ being bedrooms; _e_ was a
wash room, the like of which has never been seen before. It had not
occurred to me that the mill pond _m_, which came to the very corner
of the building, would furnish the boys a complete system of city
water-works. At _g_, in the corner of this room, they had cut a hole
in the floor and nailed slats across upon the under side of the
timbers, making a depressed floor for a shower bath. This was directly
over a stream of water which issued from the mill pond. Hanging from
the ceiling over this spot was the nozzle of a garden hose. The other
end of this hose ran into the mill pond. The nozzle was capable of
delivering either a stream or a shower, according to which way it was
twisted in its socket. It was also capable of shutting off entirely the
flow of water. The boys asked me to hold my hand in the shower, and to
my astonishment it was warm. "What, pray, is your heating system?" I
inquired. They invited me to go and see. Moored outside in the mill
pond at the corner of the building was our motor boat, which the boys
were allowed to use freely and which they understood as well as any one.

[Illustration: Fig. 108]

They said that ordinarily they used for the shower the cool water of
the lake, which they much preferred, and which ran of its own accord,
the lake being a trifle higher than the nozzle of the shower, but
knowing my antipathy for the cold bath they had slipped the end of the
rubber hose over the outlet pipe of the pump which served to cool the
gasolene engine in the boat. The engine uncoupled from the propeller
was heating and pumping water for my shower bath, and I immediately
accepted the invitation to enjoy it.

Certainly no bath was ever more delightful than that one, coming, as it
did, at the close of a hot, dirty ride from the city.

I had hastened the bath, because it was already dusk and I had no
candle at the mill, but suddenly the room lighted up as if by magic.
I saw then what had before escaped my notice, a miniature electric
lamp, six-volt, two-candle-power, tungsten, such as are used for tail
lights on automobiles. Since tungsten requires about 1.25 watts per
candle-power it was a 2.5-watts lamp, and since it was adapted to six
volts it would take about four tenths of an ampere.

6 volts × .4 ampere = 2.4 watts. The little wire filament looked to be
about 1.5 inches long. Its resistance must have been 15 ohms.

6 volts/15 ohms = .4 ampere.

A battery of five cells was used to furnish electric current for the
lamp. Lamps were installed in the bedrooms also and were not intended
to be used more than half an hour at a time. Dry battery cells are
excellent for this purpose, and for so small a current the cheapest
dry cells are as good as the more expensive ones. These cost fifteen
cents a cell. They were connected by short pieces of bare copper wire;
No. 18 "in series," as shown in Fig. 109. A wire ran from the central
(carbon) binding post of one cell to the marginal (zinc) binding post
of the next cell. This battery was placed on a shelf in a convenient
place. A bare copper wire, No. 18, was attached to the carbon post at
one end of the battery and another to the zinc post at the other end
of the battery, and these two wires ran to all the rooms where lamps
were placed. The wires were fastened up on the walls by staples, taking
care that they should nowhere come in contact with each other and
"short circuit" the battery. Whenever it was necessary for one wire to
cross another, small pieces of pasteboard were tacked up to prevent
their touching each other. The lamps _L_ (Fig. 109) were connected
to these wires "in parallel." They cost forty cents apiece, and the
miniature sockets, into which they were screwed, cost five cents each.
One of these sockets was screwed to the side of the door casing in each
bedroom. Wires were attached to the line wires, simply by twisting them
together. One of these came down to one side of the socket and the
other came to the other side of the socket through a switch, _s_, made
of a strip of sheet zinc. The cost of the entire installation was as
follows:

    5 dry cells at 15c                          .75
    5.2 cp., 6-volt tungsten lamps at 40c      2.00
    5 miniature wall sockets at 5c              .25
    Wire, etc.                                  .20
                                               ----
                                              $3.20

[Illustration: Fig. 109]

Suppose each lamp is used thirty minutes a day for 100 days, making a
total of fifty hours. There are five lamps, making a total of 250 lamp
hours. Each lamp takes .4 of an ampere, making a total of 100 ampere
hours. The lamps are operated at six volts, making a total of 600 watt
hours.

        100 days
         .5 an hour each day
        ---
         50 hours
          5 lamps
        ---
        250 lamp hours
         .4 ampere for each lamp
        ---
        100 ampere hours
          6 volts
        ---
        600 watt hours

This amount of electrical energy would cost six cents if generated
by a dynamo. It is generally stated that electricity costs fifty
times as much if generated by battery as by dynamo. In this case the
battery actually did serve for the whole season of 100 days and was not
exhausted at the end of the season.

Indeed, since that season, the boys have found that battery cells
which had been too much exhausted for use on the engine served very
well on the lamps. By use the cells lose, not much in voltage, but in
the ability to furnish sufficient quantity in amperes to make the hot
spark required for igniting the mixture of gasolene and air in an
engine cylinder. When they have been discarded for use with the engine
they may still furnish the small amount of current required for the
lamps--provided not too many lamps are used at one time.

The dynamo current is always surprisingly cheap when compared with
that produced by a battery, but, on the other hand, we are never as
economical in the use of the dynamo current as we are with that of the
battery.

If all five of the lamps in the above equipment were lighted at the
same time and kept burning for half an hour, the battery would run down
rather badly and would not fully recover. But if one only is used at a
time and for not more than thirty minutes, or if more than one is used
at a time and for a proportionately shorter period, the battery will
receive no damage.

Dry battery cells may be purchased for either twenty-five cents or
fifteen cents each. The chief difference is that the former are
capable of giving larger current than the latter, when working against
very small resistance. For example, the former may give twenty to
twenty-five amperes on a short circuit, that is, connected directly
with the ammeter without other resistance, while the latter may give
not more than six to ten amperes under similar conditions. For most
purposes, other than igniting gasolene engines, in which dry cells
are used, an exceedingly small current is required. The electric
bell, for example, may not require more than .2 of an ampere and that
intermittently. Now it is found by experience that the dry cells which
are only capable of furnishing on short circuit six to ten amperes will
last quite as long in bell work as one which may give on short circuit
twenty to twenty-five amperes. Hence it is good economy to buy them.

"What a fine sitting room you have here! (Fig. 107, _f._) When do you
expect to fit it up?" said I. Instantly reminding myself, however, that
boys do not want a sitting room, I inquired what they intended to use
this fine, large room for. They told me that they had plans for making
a machine shop out of that. The idea had been suggested by a counter
shaft which still hung from the ceiling, and they had discovered that
the old mill wheel would still roll over if the penstock were repaired.
I replied that I would see what could be done about that sometime.

On the next day matters concerning the motor boat engaged our
attention.




X

HOW ELECTRICITY FEELS


What is more fickle and yet more fascinating than a motor boat? On the
morning after my arrival at Millville the boys wanted me to go out with
them in the motor boat on the mill pond, as our beautiful little lake
is called.

Each one took a hand at trying to start the boat, but although she had
acted perfectly well the day before, on this morning no one could get
a single explosion. The switch was closed. The gasolene was turned on.
The carburetor valves were set at the mark. The spark coils responded
with their familiar buzz. She had been primed and, when she had refused
to respond to this treatment, the pet valves were opened and the wheel
rolled over several times to sweep out the cylinders. But absolutely
nothing moved her--neither coaxing nor gibes. Suddenly some one rolled
the wheel over for the five-hundredth time and she started and behaved
well all day.

All this would not have given us the slightest aggravation if we could
only have found out what was the matter and what it was we finally did
to correct it. But this we shall probably never know, and hence we are
worshippers of the motor boat while we continue to distrust it and
complain of it.

While the boat was running one of the boys noticed that a binding
post at the end of one of the spark plugs seemed to be loose. He
inadvertently put out his hand to tighten it and received a terrific
shock. This raised the question among the boys, why one gets a shock
from some of the binding posts in the electrical equipment but not from
others. I suggested that we run in and call at the house to get my
portable measuring instrument (Fig. 110) and a little lunch, and then
go up to the upper end of the lake and take our time in examining the
electrical equipment of the boat.

[Illustration: Fig. 110]

The engine had two cylinders. There were two batteries--one for each
cylinder. Each battery consisted of five dry cells like the one
represented in Fig. 111.

"Now, why don't I feel the electricity when I touch the binding posts
of this dry cell?" inquired one of the boys as he handled one of the
cells which we had taken out. "Well, I'll give you two reasons why do
you not feel it," said I. "First, because you were touching only one
binding post at a time. You must touch both of the binding posts of
the battery cell at the same time, so that the electric current may
pass from one post to the other through your body. Second, even when
you do touch both binding posts at the same time you feel no current,
simply because you offered probably about 100,000 ohms of resistance
to the passage of the current and inasmuch as the one cell exerts only
1.5 volts of pressure, it could send only about .0000015 of an ampere
through you. This you cannot feel.

[Illustration: Fig. 111]

    (1.5 volts)/(100,000 ohms) = .0000015 amperes.

"I now connect my instrument as a volt meter between the binding posts
of the cell and you see it indicates 1.5 volts, and when I connect it
for an instant as an ammeter you see it indicates twenty amperes. That
is twice as much as they use for executing criminals by electricity.
So you see if you could reduce your resistance sufficiently this one
battery cell might kill you. Some people have less resistance than
others. The resistance of the body is chiefly in the outer skin. If
one's hands are dry and his skin has been made tough and horny by hard
work, he has many times the resistance of one whose hands are moist and
whose skin is thin and tender.

"Suppose we select the tip of the tongue as the portion of the body
which will offer the least resistance and will be most sensitive to
slight electric currents. Let us then connect one dry cell with the
ammeter and place the tip of the tongue between the bare ends of the
wire at _T_ (Fig. 112).

[Illustration: Fig. 112]

"I have connected the ammeter so that it will indicate thousandths of
an ampere, and you see that the needle moves only slightly. We cannot
call it more than .001 ampere." Each boy in turn tried sending the
current through his tongue and each tried to tell how it felt. One
said it tingled, another said it felt warm, another said it tasted
sour and the other said he did not feel or taste anything. "Well," I
said, "whether you feel anything or not one-thousandth of an ampere is
passing through your tongue and you are offering fifteen hundred ohms
of resistance.

    (1.5 volts)/(1500 ohms) = .001 ampere

"Your hand offers nearly seventy times as much resistance as your
tongue. Suppose we try increasing the voltage, or pressure, of our
electric current. We will connect in series the ten cells, making
a battery which you see by the volt meter gives fifteen volts of
pressure. We now find that having ten times the pressure it sends ten
times as much current as formerly through the tongue."

    (15 volts)/(1500 ohms) = .01 ampere

Each one now testified that the battery sent all the current he cared
to take through his tongue. If they send one thousand times as much as
that through a criminal no wonder it kills him. It produces a twitch
when the contact is first made, afterward a decided sensation of warmth
and acid taste.

If we should increase the voltage tenfold more, say the 110-volt dynamo
current (direct current), and touch the bare conductors with our hands,
the ammeter would indicate about .001 ampere. That is, although this
current has about seventy times as much push, or voltage, as a dry
cell, no more electricity passes through the fingers than did through
the tongue in the preceding experiment with one cell. The fingers offer
so much greater resistance.

By wetting the fingers and pressing them firmly upon the bare wires,
we may make the ammeter read .01, that is, we may increase the current
tenfold by reducing the resistance to one tenth. But there is nothing
disagreeable about the feeling. If the same experiment is tried with
the 110-volt alternating current, although the quantity of current
which passes through the fingers is the same as before, the tingling
is more perceptible than in the case of the direct current. If we
join together seventy-five dry cells, giving a voltage of 112, and
press the bare wires with our wet fingers, the ammeter will indicate
.01, but there is no tingling sensation, merely a slight warmth. The
battery current, being continuous, causes no twitching of the muscles
while the contact is closed. The direct current dynamo furnishes a
slightly pulsating current. Hence, one may tell by the feeling whether
an electric current comes from a battery or a direct current dynamo.
The alternating-current dynamo gives a surging of electricity back
and forth in the wires, and this may be distinguished from the direct
current by its feeling; when, however, the number of alternations per
second is increased very greatly, one may receive through the body
considerable quantities of electricity without feeling it. With a very
high frequency current one may put himself in circuit and light a
16-candle-power lamp without any disagreeable sensation.

The outer skin is our chief insulation. If it is dry and well toughened
by work it offers a resistance of over 100,000 ohms upon gentle
contact. A wounded spot, or places like the tongue with moist, thin
skin, may offer a resistance as low as 500 ohms. If one has a pin prick
or a splinter in his hand which he cannot locate, he may hold one bare
wire of a 110-volt alternating circuit in one hand and move the other
bare wire about on the suspected region, and know when it reaches the
spot by a tingling sensation.

[Illustration: Photograph by Helen W. Cooke. Feeling Electricity]

One may touch lightly the 220-volt direct current and scarcely note any
difference between this and the 110-volt direct current, because one is
not very sensitive to the difference between .001 ampere and .002
ampere passing through his body.

    (100 volts)/(100,000 ohms) = .001 ampere,
     and
    (200 volts)/(100,000 ohms) = .002 amperes

Physicians treat certain ailments by the use of the electric current.
For this purpose they invariably use a pulsating or alternating current
and reduce the resistance by using metal handles and wet sponges for
contact with the skin, but even so a very small amount of current
passes. The moderate twitching of the muscles seems to be the end
sought.

Men who are supposed to be killed by electric shocks often die from
other causes. A man perching upon an electric light pole, repairing
wires, may come in contact with a wire charged, say, to 2000 volts. He
may receive a shock which throws him in an unconscious condition across
another live wire which burns its way into his flesh, or he may fall to
the ground and be killed by the fall. A workman may hold a tool so as
to short circuit a current through it, making it red hot in his hands.
So many men who have been shocked into unconsciousness by high voltage
currents have recovered consciousness later that we cannot say how much
current is required to kill a man. For the execution of criminals 1800
to 2000 volts are used, and by special metal contacts ten to fourteen
amperes are forced through the body.

The first execution of a criminal by electricity was performed in Sing
Sing Prison, New York State, in 1890. There was at that time a hot
controversy among experts over the question whether death, or merely
unconsciousness, could be produced by electricity. To be on the safe
side the legislature passed a law requiring that the electrocution of a
criminal should be followed immediately by the dissection of his body.
Only six states out of forty-nine have thus far adopted that method
of capital punishment, five have abolished capital punishment, and
thirty-eight still prefer hanging to electrocution. But it should be
remembered that it is amperes, not volts, that kill. One often hears
the meaningless expression, "he received 2000 volts into his body."
The volts indicate the pressure, analogous to pounds per square inch
of water pressure. Amperes of electricity are analogous to gallons of
water. It is possible to have exceedingly high voltage of electricity
without amperes enough to do damage. When one holds his finger near to
a rapidly moving leather belt and a stream of sparks passes between the
finger and the belt, the voltage may be 50,000 or even 100,000, but
the quantity in amperes is too small to do any damage or even produce
much sensation. A similar thing is true when one produces sparks by
rubbing a cat's back, or lights the gas by a spark produced by rubbing
the feet upon a carpet. Such sparks are miniature lightning discharges.
The real lightning does damage because it furnishes quantity,
measurable in amperes, as well as extremely high volts of pressure.

At this point I was reminded by the boy who had received a shock from
the engine that morning that he had touched only one binding post.
How then had he closed a circuit through his body, and how could he
receive such a terrible shock when there were only a few battery cells
to produce the electric current. I replied that he had the distinction
of having encountered about a 5000-volt current. In the language of the
newspapers he might say, _Took 5000 volts and still live._ We must next
proceed to show how he really did close the circuit and how the spark
coil enables a battery of a few dry cells to produce exceedingly high
voltages.




XI

THE ELECTRICAL SPARKING EQUIPMENT FOR A GASOLENE ENGINE


Under the shade of a great sugar maple, with Millville Lake spread
before us, we took apart and examined the entire equipment for
producing the electric sparks to explode the mixture of gasolene and
air in the cylinders of our motor boat. The engine has two cylinders.
For each cylinder there is a separate battery and spark coil. Inasmuch
as the electrical outfit is duplicated for each cylinder it will be
necessary for us to consider the case of one cylinder only.

When this engine is running, 700 explosions per minute are produced in
each cylinder. In one-twelfth of a second the following four events
take place:

1. The cylinder is swept clear of the products of combustion formed by
the last explosion.

2. Four drops of gasolene are vaporized and mixed with one quart of air
and pushed into the cylinder by the pressure of the atmosphere.

3. This mixture is compressed by the piston in the cylinder to about
one-fifth its original volume.

4. The mixture is heated to its kindling temperature, which is above
2000 degrees. It then burns with a sudden expansion, which drives
the piston before it and pushes the crank which is concealed in the
lower end of the cylinder half-way around. The crank is attached to
the shaft, which carries the fly-wheel upon one end and the propeller
wheel upon the other end. The momentum of the moving parts--chiefly
that of the fly-wheel--suffices to accomplish the remaining half of the
revolution.

That any machine could be devised which could repeat these four events
700 times a minute was unthinkable a few years ago.

The first men who thought that a gasolene engine could be a practical
thing were considered visionaries, but now they are found to be more
practicable than steam engines. They are so efficient that they compete
with the steam engine upon its own ground, and, in addition, they
have opened up regions of usefulness which the steam engine can never
exploit. So far as we can see, they have a permanent monopoly of the
navigation of the air.

It is with the fourth event mentioned above, viz., kindling the
explosive mixture, that we are now concerned. The high temperature
required for this is obtained by forcing an electrical current against
resistance.

Five dry battery cells would very readily heat a short piece of fine
wire to a sufficiently high temperature to explode the mixture, but
it is impossible to alternately heat and cool a wire twelve times a
second. It is too slow an operation. The only other method known at
present is to imitate the lightning and force an electric current
against the resistance of the air with sufficient power to produce the
required heat. This, however, requires an extremely high voltage--at
least 5000 volts, and our battery of five cells has not more than seven
and a half volts of pressure. The interesting question then is, how
does the spark coil enable us to raise the voltage from 7 to 5000.

To help toward an understanding of the matter I took seven small wire
nails which I found in the boat--they were sixpenny finishing nails. I
then took two or three yards of No. 24 insulated magnet wire, such as
is used upon electric bells, etc. I use it more often than any other
wire, and always have some about the boat. I fastened one end of this
wire to one of the binding posts of a dry cell (Fig. 113), _a_, and
attached branches _c_ and _d_ to it. The other end, _b_, was left
free to act as a switch for closing the circuit by touching it to the
remaining binding post.

[Illustration: Fig. 113]

[Illustration: Fig. 114]

[Illustration: Fig. 115]

One boy then touched the bare ends _c_ and _d_ to the tip of his
tongue, while I touched repeatedly the binding post with _b_. There
was, of course, no sensation. We now wound a portion of the wire upon
the bundle of nails, laying on about fifty turns. (See Fig. 114.) The
tongue was now placed at _T_ and _b_ was touched a few times to the
free binding post. A very decided shock was felt, not while the end
of the wire was resting upon _b_, but at the instant of touching and
again at breaking the connection. The shock was noticeably stronger at
the instant of breaking than of making the connection. There was also
a spark formed when the connection was broken, which did not appear
before the coil was made. We next wound on more of the wire--about
fifty more turns (Fig. 115). When now connections were made and broken
at _b_ the tongue at _T_ felt a much more decided shock, and a larger
spark occurred at _b_ when the circuit was broken. Both the tongue
and the spark indicate that the voltage is creeping up very rapidly
in this series of experiments. We next connected two cells in series,
then three, four, and finally five cells in place of the one. The spark
grew larger and "fatter," as the boatmen say, with each addition of a
cell. It was not pleasant to use the tongue in the experiment after
the number of cells exceeded two. I removed the branch _d_ from the
wire _b_ and connected it to the binding post, as shown in Fig. 116.
I then removed the crystal from my watch and poured into it a little
gasolene. I rubbed the ends of _b_ and _d_ together over this, and
when they separated the spark which was produced would not light the
gasolene. We had made a coil which produced a spark that looked like a
miniature flame, but still was not hot enough to set fire to gasolene
vapour. It simply needs more iron in the core and more turns of wire
about it. Bringing the ends of the wires together and separating them
is somewhat like drawing an arc with the arc light carbons. It requires
a vastly higher voltage to make a spark jump across an air gap than it
does to lead it across thus.

[Illustration: Fig. 116]

The kind of coil we have made (only larger) is very much used in houses
as a gas-lighting coil (to be described later). It is very much used
also for exploding gasolene engines. It generally passes under the name
of the "make and break" coil. The revolving shaft of the engine is made
to push together the ends of the wire and separate them at the right
instant to make the spark for explosion. Of course this is done inside
of the engine cylinder.

That type of coil does not offer resistance enough to protect the
battery, and dry cells soon run down if used with it. The coils that
we have in this boat are somewhat different from that, the details of
which we cannot now entirely explain.

They offer enough resistance to cut the current required of the battery
down to one third what the "make and break" coil would take and at the
same time they raise the voltage so much higher that the spark will
jump across an air gap without being led across as an arc. Hence they
are called "jump spark" coils.

[Illustration: Fig. 117]

It will be remembered that when we were studying the dynamo we produced
an electric current by moving a magnet. We may now add that an electric
current may be produced by simply changing the strength of a magnetic
field. The coil that we have just made creates a magnetic field in
the region about itself whenever a current is passing through it. The
tongue at _T_ (Fig. 117) detects an extra current while the magnetic
field is being produced, or while it is dying away, or it will detect
any slight variations in the strength of the current which produces
the magnetic field. It is customary to distinguish between these two
currents. The battery current which produced the magnetic field is
called the primary current and the current which is detected by the
tongue is called the secondary current. The primary current in our
experiments had only a few volts of pressure, from one to seven. The
secondary current had many volts, as indicated by the spark. If we
rub the end of the wire _c_ across the binding post under _b_ (Fig.
117) no spark occurs. The current does not in this case go through
the coil, and no secondary current is produced. Whenever we touch the
wire _b_ to that post we have, in addition to the primary current
which has not voltage enough to produce a spark, a secondary current
flowing in the same wire at the same time and having voltage enough to
produce a spark. The primary current is continuous while the contact
is closed; the secondary current is momentary, as the tongue detects,
and is produced only while changes are being made in the strength of
the magnetic field. We will now take another piece of wire and wind
upon the coil about two hundred more turns, leaving this outer coil
wholly disconnected from the inner one, (Fig. 118). I connect _c_ and
_d_, the terminals of what we may call the secondary coil, with my
measuring instrument and I connect _a_, one of the terminals of the
primary coil, with the battery. I then rub _b_, the other primary
terminal across the free binding post of the battery. At the instant
of closing the primary circuit--that is, of building up the magnetic
field--a secondary current is induced in the secondary coil, which
lasts for only an instant, too brief a time for the needle to measure
it, although its motion indicates both the presence and the direction
of the induced current. While the primary circuit remains closed--that
is, while no change is occurring in the strength of the magnetic
field--the needle returns to zero, indicating no secondary current. But
when now the primary circuit is broken and the magnetic field loses its
strength, the needle indicates a momentary current in the secondary
coil and _in the opposite direction from what it had been at first_.

[Illustration: Fig. 118]

If, therefore, I rapidly make and break the current at _b_ I produce an
alternating current in the secondary coil. I will connect _c_ and _d_
with a miniature lamp and, resting a coarse file upon the free binding
post, I will rake the end of the wire _b_ up and down upon this file so
that, as it dances along upon the file, it will rapidly make and break
the primary circuit, and therefore rapidly change the strength of the
magnetic field. You notice that the lamp lights up moderately well. It
is being lighted by an alternating current. I move the wire a little
more slowly and you see the flicker of the alternations. According to
the label upon the lamp it requires ten volts, and our battery could
not give that. We have therefore "stepped up" the voltage as we say and
we have a veritable step-up transformer.

In this case the primary and secondary circuits are entirely separate.
It is a familiar fact that different electric currents may pass through
the same wire at the same time without apparent conflict. We send
numerous telegraph despatches through the same wire at the same time.
It is quite as easy for several pairs of persons to telephone over the
same wire at the same time as it is for those same several pairs to
carry on separate conversations in the same room at the same time, at,
say, an "afternoon tea." We may use the same wire at the same time to
carry direct and alternating currents. This fact was first discovered
in 1902 by Bedell of Cornell University.

Primary and secondary currents do not require separate primary and
secondary coils to convey them. They may or may not be connected into
one continuous coil. It is quite immaterial whether they are connected
or not so long as they are in the same magnetic field. Indeed, it seems
that the field outside of the wire may be quite as important as the
wire itself.

[Illustration: Fig. 119]

We have now 100 turns in the primary and 200 turns in the secondary
coils. Let us connect _b_ with _c_ so as to make one continuous circuit
of 300 turns. Let us then put a branch upon _b_ to connect with the
battery, thus having 100 turns for the primary circuit, and put a
branch upon _a_ to connect with the lamp, thus having 300 turns upon
the lamp, (Fig. 119). When now we rub _b_ upon the file, as before,
the lamp lights up more brightly than before, indicating that we have
stepped up the voltage still higher. Varying the strength of the
magnetic field induces a secondary current and the voltage of the
induced current is determined, in part, by the number of turns in the
secondary circuit. If what we have been saying is true we ought to be
able to get these same results from an electric bell. To test this we
connected wires with _a_ and _c_, (Fig. 120), and since I knew that
the secondary current at _S_ would be too severe for the tongue we
decided to feel it with the hands. For this purpose we want a larger
surface than the wires themselves offer for contact with the hands,
and so I twisted the bare end of each wire around an iron spike. The
four boys then arranged themselves in line, joining hands, and the
boy at each end of the line held a spike in his free hand. Thus we
had put the enormous resistance of four human bodies joined in series
in the secondary circuit. When now I connected two dry cells with _a_
and _b_ (_P_, Fig. 120) the hammer of the bell acted, like the file in
the former case, as interrupter of the primary circuit. As it rapidly
made and broke the primary circuit, it produced rapid changes in the
strength of the magnetic field and thus induced a secondary current
which the boys all felt. The fact that it forced its way through four
bodies shows that its voltage was high. The high voltage was also
indicated by the spark which always occurred in the bell. The primary
circuit in this case has not more than three volts while the secondary
has more than a hundred. We have it in our power to give the secondary
current almost any voltage we choose, with this limitation _each
increase in voltage necessitates a proportional sacrifice of quantity_.
The watt power induced in the secondary circuit cannot exceed that
contributed to the primary circuit--indeed cannot quite equal it since
there is some loss in heat.

[Illustration: Fig. 120]

Suppose we operate a bell on a primary current having three volts
and .25 ampere, that is, .75 watt. Suppose then the voltage of the
secondary current is stepped up to fifty times three, or 150 volts. The
quantity of secondary current will be found to be somewhat less than
one fiftieth of .25 or .005 ampere. The 150-volt alternating current
from the bell is more tolerable than that from a 150-volt dynamo,
because the quantity is limited in the former case.

Our spark coil has a vibrator which acts precisely like the hammer of
the bell to make and break the primary circuit and thus make rapid
changes in the magnetic field produced by the primary coil. The primary
coil of the spark coil is many times larger than the coil of the bell,
that is, it contains many more turns of wire. It has much more iron
in the core. We use upon it five cells instead of the two cells upon
the bell. The result of all this is that we have a much more powerful
magnetic field than that in the bell and many more watts of energy
from which to induce a secondary current. Now the number of turns
employed in the secondary circuit of our spark coil is very great,
stepping its voltage up to thousands where the bell induced hundreds.

[Illustration: Fig. 121]

Suppose we now repeat our experiment in which we tried to light the
gasolene in the watch crystal, using now the spark coil of the boat
instead of our small "home-made" coil. In Fig. 121, B is the battery
of five dry cells. _S_ is a switch. _V_ is the vibrator, which, like
the hammer of an electric bell, makes and breaks the primary circuit.
Of course the coil has a core of iron, although that is not here
represented, and, of course, the coil has many hundred turns instead
of the few here represented, and of course also it is built up of many
layers instead of one as here represented. The secondary has very many
more turns than the primary, but those in which the primary current
passes are common to both circuits. There is also a condenser--not here
represented, and not to be described in this book. The result of all
this is that the secondary circuit has a voltage of between 5000 and
10,000, and a spark jumps across the gap at _c_ between one sixteenth
and one eighth of an inch long. This spark is hot enough to light the
gasolene which I have put in the watch crystal at _c_.

[Illustration: Fig. 122]

Let us return to the bell for a few minutes. I have here a miniature
lamp which requires 10 volts and .1 ampere, that is, 1 watt, which I
will connect at _S_ (Fig. 122). When now I close the primary circuit
with two cells at _P_ you notice that the lamp lights up, but faintly.
It is not receiving .1 ampere. Remember we have only .75 watt at our
disposal and this lamp requires 1 watt. Hence it is getting only three
quarters enough energy. We connect in a third cell and now it lights up
to full brilliancy. The resistance of this lamp must be about 100 ohms.

    (10 volts)/(100 ohms) = .1 ampere

The resistance of the four boys might have been 60,000 ohms, and the
voltage of the secondary circuit might in that case have been, say, 150.

    (150 volts)/(60,000 ohms) = .0052 ampere

How does it happen that the secondary current had a pressure of 150
volts on the boys but cannot supply even the 10 volts required by the
lamp?

Perhaps we can be brought to appreciate the answer to that question
best by asking ourselves some others quite like it.

Why did not the man who built our mill two generations ago locate it
upon the small stream that flowed near his house? The small stream was
more conveniently located for him and it has quite as much fall as he
got at the foot of this lake. We sometimes express the fact by saying
that the "head of water" or the water pressure was quite as much in one
of these cases as the other.

One boy said that the stream sometimes gives out. Another one said that
it never did have water enough to run that wheel. "Undoubtedly the
trouble is with the quantity," said I, "but I want to show you that we
cannot maintain the pressure unless there is sufficient quantity back
of it."

[Illustration: Fig. 123]

In Fig. 123, suppose _A_ represents a small, slim tank of water three
feet high. The water-wheel _W_, requires one gallon of water a minute
pushed along by a three-foot head of water pressure to run it. The
supply pipe _S_ is bringing into the tank not more than one quart of
water per minute. A gate at _R_ enables us to regulate the flow of
water, as we regulate the flow of electricity, by using more or less
resistance. Now it is evident that if we close the gate, or partially
close it, and allow the tank to fill with water, we may then open the
gate and run the wheel for a short time, but the level of the water in
the tank soon begins to fall and the pressure grows less and the wheel
stops moving. It is just so with all generators of electric current.
If we take from them more than they can supply continuously the
voltage falls. This is notoriously true of dry cells. Like the water
tank represented in Fig. 123, they "run down" if used continuously
to furnish, say, one ampere of current, but they may furnish it for
a short time, the voltage rapidly falling meanwhile. Then if given a
short rest they "pick up" and will again furnish full pressure. The
voltage of a dry cell falls somewhat when it is required to give the
very small amount of current required to actuate a volt meter, say .015
ampere. Hence, our volt meter will not quite correctly show what the
voltage of a single cell would be on open circuit. Notice that, when
I put one cell upon this volt meter the needle shows 1.42 volts; but
when I put four cells in series upon it the needle indicates six volts,
as nearly as we can read it. That is, the voltage of each cell in this
case appears to be 1.5. What has increased the voltage of a cell from
1.42 to 1.50? Simply this: when .015 ampere, the amount required by
the volt meter, was taken from one cell it reduced its pressure, but
when a multiplier with ten times the resistance was added we secured
our reading by using only .006 ampere of current, and this did not
appreciably reduce the true pressure of the cells.

The induced current from our bell when held back by 60,000 ohms
of resistance in the four boys was able to push with 150 volts of
pressure, and .0025 ampere passed without noticeably reducing this
pressure, but when the same current was held back by only 100 ohms in
the filament of the lamp nearly forty times as much current passed, and
the pressure dropped to something less than ten volts.

"We will try an experiment to show how the voltage will suddenly fall
when we reduce the resistance of your four bodies.

[Illustration: Fig. 124]

"Fill these two empty tin pails in which our lunch was brought with
water from the lake and sprinkle in the salt left over from the lunch.
Now twist a bare copper wire around the bail of each pail and connect
these with the bell so as to get the induced current from its magnet.
(See Fig. 124.) Let the two pails of water be the terminals of the
two wires at _S_. Now you four boys wet your hands in the water and
then join hands, and those at the two ends of the line put your free
hands upon the outside of the pails of water while I close the primary
circuit. You of course feel the current just as you did when you held
the spikes in your hands in a former experiment. But now you two end
boys put your free hands into the salt water, and you instantly get a
very smart shock. The resistance is no longer 60,000. It has dropped
way down to 2000, and if the voltage had remained at 150 you would
have received a terrible shock, but the voltage has dropped down to
five. It is as though you had been pushing very hard against a post and
it suddenly gave way. You cannot push against a thing which offers
no resistance. So the voltage falls when resistance is reduced, and
particularly if the source of supply has very little capacity. Here
is another experiment you must try when you go back to the city. At
a certain water faucet in my laboratory the pressure is disagreeably
high. The water flows with great force and spatters badly. We can
easily reduce the pressure so that the water will flow in a limpid
stream. Fig. 125 shows the situation; _f_ is the faucet, and in the
pipe underneath the sink there is a stop-cock _c_. This may be adjusted
permanently so that the faucet _f_ will act pleasantly. The same
thing is represented again at the gas stove. Let _f_ in the Fig. 125
represent a gas cock at the stove. Suppose the pressure is so high that
the gas flames pass more gas than is readily consumed. It is possible
to adjust a stop-cock like c further back in the pipe so as to produce
hotter flames, get rid of the poisonous fumes of half burned gas, and
cut down the monthly gas bills one half.

[Illustration: Fig. 125]

"My garden hose will usually throw a stream across the street, which
is very desirable when one wishes to sprinkle the street, but this
pressure is disastrous when I wish to sprinkle the flowers. Turning
down the stop-cock at the nozzle makes it shoot a smaller stream but
more spiteful in pressure, knocking the flowers to pieces and washing
the soil away from their roots. But if I partially close the stop-cock
at the side of the house where the hose is attached I may have the
stream of water flow as gently as I choose.

"I should meet precisely the same situation if I tried to ring an
ordinary electric bell by a 110-volt current, and I should use the same
method of overcoming the difficulty.

"The great virtue of the dynamo is that it can furnish a large supply
so that the voltage is kept constant on a great flow of current.

[Illustration: Fig. 126]

"I have not forgotten the question, but have tried to work toward its
answer all this time. The question is, why did Ernest get a shock this
morning when he touched only one binding post, and when the battery
of five cells is not capable of giving shocks to any one who touches
its binding posts directly? We need one more diagram to give the final
answer. In Fig. 126 _e_ represents the binding post from which the
shock was received. _B_ is the battery of five cells, _C_ is the
spark coil, _G_ is the engine cylinder, _f_ is the spark plug. When
one wishes to start the engine he closes the switch _S_. This makes a
continuous conductor from the battery to the metal cylinder itself. As
the engine rolls over it closes the gap in the conductor at _d_ for an
instant. The primary circuit is then completed and the current passes
from _B_ to the cylinder, through the metal of the cylinder to _d_,
then to the coil _C_, where it passes through a portion of the coil and
then back to the battery. The vibrator on the coil causes the magnetic
field to rapidly vary in strength. This induces a secondary current in
the whole coil which, because it passes through a very great number
of turns, has a high voltage. This passes from _C_ through _B_ to the
base of the engine, then up the walls of the cylinder to the plug _f_,
then jumps across the gap at _a_, causing the spark which explodes the
mixture of gasolene and air in the cylinder. The spark plug _f_ is
porcelain--an exceedingly good insulator. Through the centre of this
passes a wire from _a_ to _e_. The current passes up this and back to
_C_. Now the engine rests upon the floor of the boat, and Ernest stood
upon the same floor. The wood of this floor when dry and clean is a
very good insulator, but when wet, and particularly when wet with water
that has ever so slight an amount of any salt in solution, it becomes
a conductor for such high tension currents. When therefore Ernest,
standing upon the floor of the boat, touched the binding post, _e_,
this induced current of high voltage found it about as easy to pass
from the metal of the engine cylinder through the wood to his body and
through his body to _e_ as to jump across the short air gap at _a_.
There are two things upon which he may congratulate himself.

"1. While the coil stepped up the voltage so high it reduced the
available quantity of the current, so that the shock was a safe one.

"2. He received only a portion of the current which passed. The major
part of it passed across the gap at _a_, otherwise we should have
noticed that the engine missed an explosion when he touched the binding
post."

The only part of this electrical outfit from which one may receive
a shock is that line from _e_ to _C_. The greatest difference in
electric pressure is always to be found between the two extremities
of the electric generator; as, for example, between the carbon end
and the zinc end of the battery, the positive and negative poles of
the dynamos; the right-hand and left-hand end of this coil. Since the
right-hand end is connected by good conductors with the metal of the
engine and with the floor of the boat and through it with our bodies,
we are in the same electrical condition as the right end of the coil;
but the left-hand end and the wire connecting it with _e_ are forced
by the varying magnetic field into a very different state of electric
tension, and it is insulated from the engine and from us by the
porcelain spark plug. We say that the "difference in potential" between
the two sides of this system is 5000 to 10,000 volts.

The water in this lake flows through the stream at the other end of the
lake to the ocean. The water of the ocean evaporates to form clouds.
Clouds drift over the land and drop their rain to replenish the lake.
The difference in water level between this lake and the ocean is twenty
feet. A difference in water level is what makes it a water power and
it is what occasioned the building of our mill. This difference of
water level corresponds in our electric generators to the difference
in potential. The difference in potential maintained by our battery
of five cells when not producing current is 7.5 volts. The difference
in potential between the two ends of our coil, when the battery is
agitating its magnetic field, is perhaps a thousand times as much, or
7500 volts.

The boys took their swim in the lake and afterward, while we were all
on shore lying on the grass, they brought up again the question of the
machine-shop. They were anxious to know if I had any plans in regard to
it. I said I had been thinking about it a good deal over night but had
been waiting to hear their plans. Well, they thought it would be good
to have a turning lathe, but could not think of anything else unless it
might be a grindstone run by power. I said I had thought of a Central
Station Electric Plant. At this they all sat up.

"Hydro-electric stations are the proper thing now," I remarked. "On the
Rio Grande River in Colorado they are constructing several plants where
water power will be utilized to generate electricity for use more than
one hundred and fifty miles away. For transmitting electricity to such
a distance they step up the voltage, or electro-motive force as it is
called, to 100,000 volts.

They are harnessing the Au Sable River in Michigan to generate
electricity and transmit it at 135,000 volts e. m. f. to towns nearly
two hundred miles away. Electricians use e. m. f. for electro-motive
force, just as you boys use "exams." as slang for the motive force in
school.

Of course we are aware that since 1896 some of the water power of
Niagara had been converted into electric power to run street cars and
factories and furnish electric light and electric heat as far away as
Buffalo, twenty-six miles distant.

About $18,000,000 are now being invested in hydro-electric enterprises
even in Mexico.

By this time the boys were all standing up and staring at me, while
Harold inquired if I were talking in my sleep. "I have at any rate
succeeded in waking you all up," said I, "and what I have said is not
altogether a joke. Let me explain somewhat at length."




XII

ELECTRICITY FROM CENTRAL STATIONS


Large dynamos generate electricity very much more cheaply than small
machines can, and machines which have a full load continually produce
the current very much more cheaply than those which run upon very light
load part of the time. The largest central stations with load evenly
distributed for the whole day could furnish electricity profitably at
four cents per kilowatt hour. There are many small electric lighting
plants which furnish current from sundown to midnight only at fifteen
cents per kilowatt hour, with little profit. The transformer (Fig.
127) makes it possible to gather all this generation of electricity
for sparsely settled districts into large central stations, located
sometimes far away from the consumer perhaps, where there is abundant
power in some water-fall, thus saving the expense of coal for running
the dynamos.

[Illustration: Photograph by Helen W. Cooke. Operating the Switchboard]

A few years ago there were no central stations for this purpose. Now
according to the latest census reports there are in the United States
about 30,000 plants, including those which belong to certain cities,
that generate electricity for sale, and there are twice as many more
isolated plants to furnish light and power in factories, hotels, etc.

[Illustration: Fig. 127]

The money invested in central station business now exceeds six billion
dollars, and the annual output of electric current is sufficient to
keep eight billion 16-candle-power carbon filament electric lights
burning continuously night and day. All this has more than doubled in
the last five years. Central stations are now furnishing about five
times as much current for heating, cooking, and charging automobiles as
they did five years ago. About one third of all the central stations
depend on water power.

[Illustration: Fig. 128]

[Illustration: Fig. 129]

We might take as the type of hydro-electric central station, that
is, one which generates electricity by water-power, the Glenwood
Station of the Central Colorado Power Company. This station has
two 9000 horse-power water turbines. Each water-wheel drives an
alternating-current generator which develops 4000 volts of e. m. f.
These water wheels and generators are shown in Fig. 129. The penstocks
are to be seen coming through the back wall of the building. They bring
water at 170 foot head, or about seventy-five pounds per square inch
static (standing) pressure. Three huge transformers, each weighing
twenty-six tons, step up the e. m. f. from 4000 to 100,000 volts.
These are the cylinders shown in Fig. 130. They simply contain a great
many coils of copper wire with a vast amount of iron at the centre.
They accomplish in a large way what our spark coil does in a lesser
degree. But why go to all this expense to produce such a dangerous
and troublesome voltage? The answer briefly is, that while it is
dangerous and troublesome the expense is not so great as it would be
to supply by any other method the electric current required. Denver
and numerous other places, large and small, require electric current.
From one to two hundred miles away on the Grande River, there is
vast power running to waste. We have to choose on the one hand between
buying power in the shape of coal and distributing power plants to
those various localities where electricity is needed, and on the other
using this water-power, which is now running to waste, to generate
electricity which we may transmit and distribute throughout the one
hundred and eighty-five miles to Denver, Leadville, Boulder, Dillon,
Idaho Springs, etc. But electric energy transmitted a long distance
suffers great loss.

[Illustration: Fig. 130]

Suppose, for instance, I needed to supply fifty amperes at one
hundred-volt pressure ten miles distant from the generator, and had
a conductor the size of a trolley wire to bring the current. The
resistance of the trolley wire is one ohm for every two miles, or
five ohms. The drop in voltage is found by multiplying the amperes
of current by the ohms of resistance. Ten miles from the central
station, therefore, the drop on fifty amperes would be 50 × 5 = 250
volts. It would, therefore, be necessary to maintain a pressure of 350
volts at the generator to deliver the fifty amperes at 100 volts. The
energy supplied by the generator is 350 volts × 50 amperes = 17,500
watts = 17.5 K. W. The energy delivered to the consumer is 100 volts
× 50 amperes = 5000 watts = 5 K. W. In order to deliver fifty cents'
worth of electricity per hour to the consumer it would, in this case,
be necessary to generate $1.75 worth of electricity at the central
station. That is, about seventy per cent. of the energy generated would
be wasted in transmission. If now we decide to generate this electrical
energy at ten times as high voltage it will be necessary to transmit
only one tenth as many amperes, or five. In this case the drop in
voltage would be 5 amperes × 5 ohms = 25 volts. It would be necessary
to maintain 1025 volts of pressure at the generator to deliver to
the consumer the five amperes at 1000 volts = 5000 watts. That is, to
deliver 5000 watts in this case we must generate 1025 volts × 5 amperes
= 5125 watts, and less than 2-1/2 per cent. of the energy generated
would be lost in transmission.

If now the consumer must have his energy delivered at 100 volts, we
must introduce a step-down transformer at his end of the line which may
give him 50 amperes at 100 volts = 5000 watts. This transformer, being
small, will cause a loss of 15 or 20 per cent., but if there were a
very large amount to transform it might be done with a loss of only 4
per cent.

[Illustration: Fig. 131]

[Illustration: Fig. 132]

It is not thought to be advisable to raise the voltage at the generator
higher than 4000. This will not suffice to supply large working
currents to a greater distance than about six or eight miles. For a
distance of 10 miles 6000 volts are desirable; for 50 miles 30,000
volts; for 100 miles 60,000 volts; for 165 miles 100,000 volts; and for
200 miles 120,000 volts. Notice that in this table the voltage rises at
the rate of 600 per mile. Since it is not desirable for the generator
itself to produce a higher voltage than 4000, we must depend upon
transformers to produce these high voltages. Let us then consider,
a little more in detail, the construction of a transformer. I have
here some drawings of one which I propose that we make in the machine
shop, and use in our central station equipment in the future. We will
procure the thinnest and softest sheet iron possible and cut out of it
a lot of pieces shaped like the letter H with the dimensions shown in
Fig. 131. These are to be piled one upon another, with strips of paper
between, until the pile is 1-1/2 inches thick. Then four pieces of
board are to be bolted to the sides of these (Fig. 132). The dimensions
of each of the four blocks, is to be 7-1/2 inches long by 3 inches
wide by 1-1/2 inches thick. Upon the cross bar of the H we will wind
400 turns of No. 12 double cotton-covered copper wire, bringing out
the ends for future attachments, and then wind on 1200 turns of No.
10 double cotton-covered copper wire. The wire will fill the space
between the blocks as indicated by the diagram in Fig. 133. We will
then cut strips of the sheet iron 6 inches long by 1-1/4 inches wide,
and bridge across the ends of the H, prying open the leaves of sheet
iron and tucking them in between as shown in Fig. 134. We shall then
drill a hole at each corner and bolt them in place. Binding posts will
be placed at _a_, _b_, _c_, and _d_ (Fig. 134), and the two ends of
the No. 12 wire will be brought to _a_ and _b_ and those of the No. 18
wire will be brought to _c_ and _d_. Going through all this detail of
construction has probably made you lose sight of the essential features
of this transformer. Let us for a moment turn back and see what they
are. We have a large coil of wire 3 inches long and 7-1/2 inches in
diameter. It is composed of a coarse winding and a fine winding, which
we may designate as the primary and secondary coils, if we choose. Of
course the only reason for having different sizes of wire is so that
we may send larger currents through one than the other. The coil has
a laminated iron core, that is, it is composed of layers of sheet
iron. These layers are insulated from one another. This is essential,
although we cannot explain why now. But perhaps the most essential
feature of the transformer is that iron extends clear around from one
pole of this electro-magnet to the other. Fig. 135 represents a section
through the coil made in the plane of _e f g_ (Fig. 134). The core of
the magnet is represented as heavily shaded. The _magnetic circuit_ is
said to be closed from one pole of this magnet to the other through
the strips of iron which pass across the ends and down the sides of
the coil. The arrows show the path of the magnetic circuit. The dotted
portion shows where the copper wire may be supposed to have been cut
across. Inasmuch as the electric current is induced in the secondary
circuit by continually varying the strength of the magnetic field as
much as possible, the alternating current is the most desirable to use
in the primary. If the direct current were used an interrupter would
be necessary, which would of course produce too much sparking when any
but low tension currents are used in the primary circuit. The most
interesting and curious fact about the transformer is that the voltages
of the primary and secondary currents are in exact proportion to the
number of turns in the wire of the two circuits.

[Illustration: Fig. 133]

[Illustration: Fig. 134]

[Illustration: Fig. 135]

In our transformer the number of turns in the coil between the binding
posts _a_ and _b_ is 400 and the number of turns between _c_ and _d_
is 1200. If now we connect a 112-volt alternating current with the
binding posts _a_ and _b_, a volt meter connected across between _c_
and _d_ will show 336 volts, and if _b_ and _c_ be connected by a short
wire, bringing in 1600 turns into the secondary circuit, a volt meter
connected across between _a_ and _d_ will show a voltage of 448. Or
if, leaving _b_ and _c_ still connected by a short wire, we connect
the 112-volt alternating current to _a_ and _d_ a volt meter connected
across between _a_ and _b_ will show 28 volts, or if connected between
_c_ and _d_ it will show 84 volts, and if finally the 112-volt current
is connected to _c_ and _d_ the pressure between _a_ and _b_ will be
37-1/3.

[Illustration: Fig. 136]

The story, then, of the central station which we have chosen as a type
is briefly this: Falling water makes dynamos revolve, generating a
4000-volt alternating current. This current is sent through the primary
windings of transformers. The secondary windings of these transformers
have twenty-five times as many turns as the primary coils. This steps
up the voltage from 4000 to 100,000, making it necessary to send only
one twenty-fifth as many amperes over the lines as would be required
at 4000 volts, and reduces the loss in transmission to nearly one
twenty-fifth. At the other end of the line the current traverses the
secondary windings of transformers, and the consumer receives his
current from primary coils which may step the e. m. f. down to any
required volts of pressure, generally 110.

Now I shall be glad to have you consider whether this suggests any
practicable problems for us here in Millville.

The sun is nearly setting and I suppose the family is expecting me home.

[Illustration: Fig. 137]




XIII

ELECTRICITY FROM AN OLD MILL


Millville is only a name or rather a reminiscence. There was once a
village here, but now its population has all gone with the tide down
the river, even its ghost appears to have departed. The ruins have all
fallen, except the mill, which we propose to revivify.

I had built a summer cottage on the shore of the lake, about one mile
from the mill. The absolute stillness of the place charmed me when worn
out by the noise and heat and dirt and smell of the city. Here even the
owl twittered softly as if afraid to disturb the silence.

The silence which was such a boon to me seemed to be oppressive to the
younger members of the family. To prevent therefore their becoming
dissatisfied with the place and wishing to go to other resorts, I
planned to have some of their best friends spend much of the summer
with us, and I encouraged their plans for making use of the mill. I
will not offer this as an excuse for introducing electricity into a
sleeping valley. Indeed, electricity has always disported itself there
in the lightning, jumping from cloud to mountain peak as I have seen it
nowhere else on earth.

The next time I saw the boys they had ambitious plans indeed. The
penstock at the mill was to be repaired. The water-wheel was to
drive an alternating current dynamo. The voltage of this current was
to be stepped up by a transformer. It was to be transmitted to the
cottage and there the e. m. f. was to be stepped down again by another
transformer. My wife suggested that if it interfered with the simple
life it would have to step down and out. Harold, however, assured his
mother that they were going to simplify everything--even the subject of
electricity.

Their plans were: To light the cottage by electricity; introduce
a number of electric back logs, with coloured glass bottles; heat
the fireless cooker by electricity; pump the water for the house
by electricity; run mother's sewing machine by electricity; run
the washing machine and wringer by electricity; heat sad irons by
electricity; percolate coffee, wash dishes and run the vacuum cleaner
by electricity; operate the door bell and the telephone and wind the
clock by electricity. I was sure that if they carried out these plans
they would stay in Millville at least that summer, so I said go ahead.

We fixed the penstock. The boys estimated that 10 cubic feet of water
per second would pass through it. They said that a cubic foot of water
weighed 62.5 pounds and 10 cubic feet weighed 625 pounds. They said it
fell at the rate of 7 vertical feet a second, making 4375 foot-pounds
per second. But 550 foot-pounds per second is one horse-power, hence
this is about 8 horse-power. Since one horse-power is equivalent to 746
watts of electricity, we have, if we could generate it without loss,
said the boys, nearly the equivalent of 6 kilowatts of electricity, or
about 54 amperes at 110 volts.

There were several things they wanted to know before they could go
further with their plans.

1. How many of these electrical appliances we would be likely to use at
one time.

2. How much current each device would require.

3. How much they must allow for losses in generating the current, in
transmitting it, and in transforming it.

We assured them that we would never use more than twenty amperes, say,
two thousand watts at one time. They might install a fuse, or circuit
breaker in our line to protect their plant against a greater load from
us. I told them that they might allow 20 per cent. loss of energy at
the dynamo in converting water-power into electric-power.

I would suggest generating their current at 115 e. m. f. and stepping
it up to 460 for transmission to us, and then stepping it down to
about one hundred and ten volts for our use. They might count on about
one-third loss on our supply, that is, they would need to generate
about three thousand watts in order to deliver us 2000 watts.

I suggested making our line of No. 6 copper wire, which has a
resistance of two ohms to the mile. The distance from the mill to the
cottage is one mile, and the complete circuit therefore would require
two miles of wire, or four ohms of resistance.

If we start with 3000 watts and lose 14 per cent. in transforming we
shall have 2580 watts to transmit. If the voltage has been stepped up
fourfold there will be about 5.6 amperes to transmit which will suffer
a loss of 22.4 volts in passing through four ohms of resistance on the
line. The loss in transmission will be about 5 per cent., and we shall
have on arrival at the cottage about two thousand four hundred and
fifty watts with a voltage of 437.6. If now in stepping this down to
one fourth the voltage, viz., 109.4, we lose 14 per cent., we shall
have left something over two thousand one hundred watts, or nearly
twenty amperes.

Assuming that you are able to generate 4800 watts of electricity and
that 3000 watts must be furnished for transmission to the cottage,
you have left 1800 watts, which will give you something over fifteen
amperes at 115 volts for use in your machine shop. I suggest that
we get a dynamo which will generate both alternating and direct
current--the alternating current you will send to the cottage, and the
direct current you will have for use at the machine shop.

But how is it possible for a dynamo to generate both alternating and
direct current at the same time?

[Illustration: Fig. 138]

[Illustration: Fig. 139]

Recall that all dynamos are generators of alternating current. If the
brushes rest upon rings upon the axle they send forth alternating
current--but if the brushes rest upon commutator bars they send forth
direct current. Now we will have two sets of brushes, one pair of
which shall rest upon the rings on the axle, and they will collect
alternating current for the cottage, while the other pair will slide
over the commutator bars and collect direct current for the machine
shop. I have constructed a model which will make it plain. Here is
a piece of a broom handle (Fig. 138), one foot long, which shall
represent the axle of an armature. _a b c d_ is a stout wire which
represents the coil of the armature. In this case it has no iron at
its centre. Nevertheless it will serve as an armature having one loop
of its coil left. _e_ and _f_ are rings, sawed from a piece of brass
pipe, which fit snugly upon the axle. Another ring of the brass pipe
was sawed lengthwise, as shown in Fig. 139. These two halves are also
fastened upon the axle and one end of the wire loop, _c_, is fastened
to one of these, and the other end of the loop, _b_, is fastened to the
other half of the ring. These two halves of the piece of brass pipe
are placed so that their edges are near to each other but do not touch
on either side of the axle. The two ends of this wire loop are also
connected with the rings _e_ and _f_. A short wire connects _b_ and _e_
and another connects _c_ and _f_ passing through the wood of the axle,
as shown by the dotted line. We will now revolve this loop slowly about
its axle in a strong magnetic field. To produce this field I will send
two amperes of electricity through the coils of wire (Fig. 140), which
surround two iron pole pieces that are screwed into an iron base.
Between the poles _N_ and _S_ of this electro-magnet we will thrust
this wire loop and revolve it as an armature very slowly. Meanwhile I
connect two wires to my sensitive ammeter and let their free ends brush
along on the rings _e_ and _f_. The needle of the ammeter swings to and
fro for each half revolution of the armature, showing an alternating
current of .01 amperes. If this armature had many turns of wire instead
of this one loop, if it had an iron core, and if it should revolve at
high speed, the results would differ in degree but not in kind.

[Illustration: Fig. 140]

We will now move the wires which are acting as brushes over to the
metal pieces _b_ and _c_. When now we revolve the armature the needle
swings to the right, and just as the needle is about to swing back each
brush slides from the plate on which it is rubbing to the opposite one
and the needle gets another impulse forward. If the armature is turned
rapidly the pulses disappear and the needle stands constantly at about
.015 amperes. This then is both an alternating and a direct current
dynamo. It simply needs more iron, more copper wire, and more rapid
motion, to give us the 4800 watts of electrical energy we are seeking.

"But how shall we produce the current which we wish to send around the
spools of the field?" inquired the boys.

"Connect the field with the brushes which rub upon the commutator," I
replied. "It will magnetize its own field."

       *       *       *       *       *

As good luck would have it, we found that the ledge of rock which
furnished the basis for the mill dam was immediately underneath the
floor at the north end of the machine shop. Upon this we built up a
solid foundation for the dynamo. Our water-wheel gave a speed of 240
revolutions per minute to the counter shaft. A pulley of two feet in
diameter upon this counter shaft was belted to the pulley of one foot
in diameter upon the dynamo--thus giving its armature a speed of 480
revolutions per minute. We had to fix a governor upon the water-wheel
to keep this speed constant at varying loads. The voltage is very
sensitive to slight changes in the speed of the generator.

We had next to plan what equipment we should need for the machine
shop and to decide where to locate each machine. The first machine we
installed was a lathe adapted for use both with metals and wood. Among
the adjuncts of this were all sorts of drills, chisels, circular saws,
grinding and burnishing tools, etc. The second machine located was
a small forge with an electric fan to furnish the blast. These were
followed by a small band saw and a small planer. The fifth machine
was a big grindstone and the sixth was an emery wheel. The boys had a
long discussion, running through several days, on the question whether
these machines should be belted to the counter shaft, and thus get
power directly from the water-wheel, or whether each machine should be
operated by an electric motor attached to it.

Harold said: "Suppose I want to saw a piece of wood requiring a
horse-power, I must start an eight horse-power water-wheel which will
run a six-horse-power dynamo which will operate a two-horse-power motor
that will revolve the saw. There is a loss in each machine, and the
lighter the load the greater the loss. In order that the motor may
deliver one horse-power to the saw, it must receive from the dynamo,
say, one and one-half horse-power, and in order that the dynamo may
deliver to the motor one and one-half horse-power, it must receive
from the water-wheel, say, two horse-power. What is the matter with my
saving time and energy by sawing off the block with my own right arm?"

"But," said Ernest, "you forget that this water-wheel and the dynamo
must run all the time by the terms of our agreement with the cottage,
and they will run fairly well loaded, so that the starting of the
saw will not entail any such losses as you reckon. Furthermore the
water-power is running to waste, anyway. You simply divert its channel
when you start all this machinery. That's all. And lastly, if the saw
requires a horse-power, as you say, your right arm could not furnish
it."

"Oh," interposed Dyne, "it would take a horse-power to do it as quickly
as the machine does, but Harold simply proposes to take more time in
sawing the block and less in running the machinery. An infant can do
the work of a horse if you give him proportionally more time."

"I don't like the idea," drawled Erg, "that this machinery has got to
be kept running all the time. When will a fellow get a chance to sleep
or go a-fishing or have any vacation, with this central-station machine
shop on his hands all the time?"

I had inquired how the last two boys won their nicknames of _Dyne_ and
_Erg_ and had been informed that one was very keen about dining and
the other had a great aversion for work. They had doubtless seen these
terms somewhere in their reading of physics, but they appeared to have
forgotten their significance by a too familiar use of them. I told them
that these were sacred terms, the first being a name for the unit of
force, while the second designated the unit of work. Both boys said
that under those circumstances they would like to shed the names. The
names, however, stuck and the boys themselves might, I think, be said
to exercise a maximum of power with the least waste of energy.

This idea of running the plant continuously had evidently received no
attention hitherto and it bid fair to quench all the enthusiasm until I
came to the rescue by proposing a storage battery.

If we can procure a battery in which we may store energy, which shall
always be on draught by merely pushing a button, one which "is not
injured by overcharging nor too rapid discharging, nor even by complete
discharge"; one which is not injured by standing idle for any length
of time, either charged or discharged; and finally one which "is
practically foolproof"--we want to try it. I propose that you appoint
a committee to look into it. But at any rate this enterprise must go on
even if I have to hire a man to live in the loft of the mill and keep
the machinery going.

[Illustration: Fig. 141]

"No man in the loft," said Dyne, "while I have my rations."

"There will be no need for him so long as I can store energy here,"
said Erg, "so let the job of equipping the establishment go on in the
regular fashion."

After a long confab one evening at the mill we settled upon the
arrangement shown in Fig. 141. _D_ represents the location of the doors
and _W_ that of the windows. The equipment is designated as follows:
_A_, saw; _B_, planer; _C_, lathe; _E_, emery wheel; _F_, grindstone;
_G_, dynamo; _H_, forge; _I_, storage battery; _J_, switchboard; _K_
and _L_, counter shafts suspended from the ceiling. The water-wheel
is belted directly to the counter shaft _L_. This revolves at the
rate of 240 r. p. m. A two-foot pulley on this shaft is belted to a
one-foot pulley on the dynamo _G_, giving the dynamo a speed of 480. A
4-inch pulley on this counter shaft is belted to a 16-inch pulley on
the grindstone _F_, giving the stone a speed of 60 r. p. m., or one
revolution per second. A 32-inch pulley on shaft _L_ is belted to an
8-inch pulley on the counter shaft _K_, giving a speed of 4 times 240,
or 960 r. p. m. 12-inch pulleys on this shaft are belted to 6-inch
pulleys on each of the machines _A_, _B_, and _C_, giving them a speed
of 1920 r. p. m., and a 16-inch pulley on this shaft is belted to a
4-inch pulley on the emery wheel, giving it a speed of 3840 r. p. m.
As soon as everything was in running order, Harold took his mother
down to the machine shop and started all the machinery going at once,
and while they stood in the middle of the room I heard him explaining
to her how she might find out the speed of each machine. He said that
she must start with the grindstone, because that goes slowly enough to
count. She held her watch in hand and counted the number of revolutions
in a minute, as he directed, and found them to be sixty. Then he asked
her to judge how much larger the pulley on the grindstone was than
the corresponding one on the counter shaft. She said that she thought
it looked four times as large. He told her that she had it just right,
and explained that the shaft must move four times as fast as the stone,
or 240. "Now how fast do you think the emery wheel is going?" She
acknowledged that she had no idea.

"Well," said he, "when you get real used to it you can tell by the tone
a wheel makes just about how fast it is going."

Then he explained how she might calculate its speed by looking at the
pulleys, and she found that the counter shaft was going four times as
fast as the shaft _L_ and that the emery wheel was going four times as
fast as _K_. Hence it was going sixteen times as fast as _L_, or 3840
r. p. m. His mother said she thought that it was fascinating to stand
in the middle of the room with the slowly moving grindstone on one hand
and emery wheel moving sixty-four times as fast on the other hand and
think that they were propelled by the same water-wheel. I handed Harold
a speed indicator which I had just received, (Fig. 142), the mechanism
of which was all visible. Harold looked at it for a minute and found
stated upon it that the wheel _B_ had 100 cogs, and he very quickly
inferred that the axle _A_, whose screw threads fitted into these
cogs, must revolve one hundred times each time the wheel _B_ revolves
once. The tip end of this axle had a soft rubber cap _C_. Without
suggestion from me he soon held this rubber shoe against the end of the
axle of the emery wheel and counted, not thirty-eight, but thirty-six
revolutions of the wheel of the speed indicator in one minute. This
puzzled him and he inquired how it happened that the emery wheel made
only 3600 rather than 3840 revolutions per minute.

[Illustration: Fig. 142]

"Well," said I, "we always have to count on belts slipping some,
particularly upon very fast moving pulleys and upon very small pulleys.
Here are two belts to slip, and still you are losing only the effect
of one revolution of the counter shaft _L_ in a minute. Grind something
on the emery wheel and you will find that the belts will slip more.
In fact, grinding upon the emery wheel will compel the water-wheel to
go more slowly until its governor opens and gives it more water. The
water-wheel makes fifteen revolutions per minute and the emery wheel
goes 256 times as fast as that. One pound of resistance at the emery
wheel is like 256 pounds of resistance at the water-wheel. You notice
the same thing when you use the saw or planer, or even present a chisel
to a piece of soft wood in the turning lathe.

"The only machine here that it is important to keep running at constant
speed is the dynamo. We shall probably notice the dimming of our lights
at the cottage every time you saw a block or grind with the emery wheel
or even polish with the felt buffer, because the speed of the dynamo
will slacken for a moment and the voltage will drop a little."

In addition to sending electric current to the cottage the dynamo
was to keep the battery stored all the time. Each machine had an
appropriate motor attached to it which could run it by drawing current
directly from the battery when the water-wheel was not running. Thus
if one wanted to sharpen his pocket knife he merely closed a switch at
the lathe and used the small stone, or if he wished to sharpen his lead
pencil he put it in the lathe and applied a chisel to it.

These motors were all adapted to the 110-volt direct current and the
battery contained fifty-seven cells, each cell being rated a little
under two volts.

The boys frequently discussed possible combinations in this system.
I spent a great deal of time loafing around among them in a comatose
condition, and they talked quite as freely when I was around as when
they were alone among themselves. One day I heard Dyne say, "Suppose
we should store in a reservoir the water which comes down the penstock
during a day and store all the electricity it will generate in a day
in a storage battery, then at night let the battery run the dynamo
backward as a motor, and that turn the water-wheel backward as a rotary
pump, we should have the water in the upper reservoir to begin work
with the next morning and the problem of perpetual motion would be
solved.

"Aw, why do you want to do all that," said Erg, "when nature is doing
it for us?"

Ernest said he had a better scheme than that. He would turn the battery
current on to all the motors in the room and they would run the counter
shafts forward and the counter shafts would run the dynamo forward
and the dynamo would charge the battery, and so you could keep up the
motion perpetually if you wanted to.

"Get out your pencils," said Harold, as he took down a copy of Houston
and Kennelly. "Let us see how we would come out if we tried Dyne's
proposition for, say, twenty hours, storing the energy from the
falling water for ten hours in the battery and then using this energy
during the next ten hours for re-storing the water in the upper pond.
We will say that the water-wheel furnishes eight horse-power for ten
hours--eighty horse-power hours."

I notice it is stated in this book that small dynamos are usually
unable to deliver more than 75 per cent. of the energy impressed upon
them, and storage batteries and motors deliver about 80 per cent. of
the energy impressed upon them. The accounts would, therefore, stand as
follows:

    _Dynamo_                                _Horse-power Hours_
                                                  _Dr._  _Cr._

    To energy impressed by water-wheel             80
    By energy delivered to storage battery                60
    By loss in heat                                       20
                                                   ---------
                                                   80     80

(Assuming that the battery was able to receive all the dynamo could
give.)


                    STORAGE BATTERY ACCOUNT

    To energy impressed by dynamo                  60
    By energy delivered back to dynamo running
      as motor                                            48
    By loss in heat                                       12
                                                   ---------
                                                   60     60

    _Dynamo Running as Motor_               _Horse-power Hours_
                                                 _Dr._   _Cr._

    To energy impressed by battery                 48
    By energy delivered back to water-wheel               36
    By loss in heat                                       12
                                                   ---------
                                                   48     48

(This dynamo being a particularly inefficient motor.)

We cannot give the account of a water-wheel acting as a pump, because
such a machine has not yet been perfected. It is evident however that
if a water-wheel could be devised that should be a perfect pump, the
losses in this chain of machinery are more than half; indeed, the
accounts show them to be 60 per cent. We should, therefore, be able to
return less than half the water drawn from the lake each day, and we
should rapidly move toward bankruptcy.

"Well," said Ernest, "my proposition is more successful than that,
because it sets out to be a fool proposition."

It was first suggested by the snake who undertook to swallow himself.
Suppose the account does taper down from eighty to one, so does the
snake, but he still remains "wise as a serpent." Our account would
stand as follows:

     _Dynamo_      _Battery_      _Motors_

    36    27     27     20      20     15
    15    12     12      9       9      7
    7      5      5      4       4      3
    3      2      2      1       1       .8
     .8     .6     .6     .48     .48    .36
     .36    .27    .27    .20     .20    .15
     .15    .12    .12    .09     .09    .07
     .07    .05    .05    .04     .04    .03
     .03    .02    .02    .01     .01    .003

It is evident that while our energy would dwindle continually we should
never quite come out of the little end of the horn, since any number
may diminish by 20 per cent. of itself indefinitely.

"Let us get at something practical," said Erg. "How are we going to
furnish electricity to the cottage when the dynamo is not running? If
we put a storage battery at the cottage, how are we going to store it
having nothing but alternating current up there; and if we attempt to
transmit current from our central station battery, how are we going to
get along with the drop in the voltage?"

"I'll tell you how to do that," said Dyne. "They want 20 amperes and
the line offers 4 ohms of resistance. That means a drop of 80 volts. We
have simply to provide a subsidiary battery of 48 cells, which we may
throw in series with our 57 cells when we supply electricity to the
cottage, and then they will have the right voltage for use out there."

"Yes," said Erg, as he rolled over, "they will have the right voltage
when they use 20 amperes, but what will happen if they simply turn on
one lamp. The drop in voltage then will be (.5 amperes × 4 ohms =) 2
volts; 105 cells at 1.8 volts a cell will send out there 189 volts
minus the drop of 2 volts, leaving 187 volts upon a lamp adapted to 110
volts, and it will immediately burn out. The same thing would happen to
any single piece of apparatus if the current was turned upon it alone.
The only thing they could do if they wanted to light a lamp, say in
the middle of the night to take a dose of medicine, would be to start
up all together, all their lamps, sewing machine, wringer, dishwasher,
fireless cooker, vacuum cleaner, etc., etc., to keep down the voltage
so that one lamp would not burn out."

"I have read," said Ernest, "that they use rectifiers, which convert
the alternating into direct current, for storing batteries. These
are much used over the country. Electric automobiles run by storage
batteries, and in the great majority of communities there is no
other electric current than the alternating. So they would be
helpless without the rectifier. We should then get another battery
of fifty-five cells for the cottage and keep it stored by using a
rectifier with our alternating current.

"But all their equipment up there," said Ernest, "is adapted to the
alternating current. Of what use would a direct current be to them?"

"Well," said Harold, "it is all the same whether you have alternating
or direct current on lamps, cooking apparatus, etc., and I have
understood that they have motors which run on both alternating and
direct currents. If so, that would fix them up all right."

The boys now turned to me for the first time to inquire whether motors
could be obtained which would run on both alternating and direct
current, and I replied that small motors for running sewing machines,
vacuum cleaners, etc., were made which would serve us, perhaps not
economically, but as they were the only solution to our problem we
could get along with them.

"Why don't they have alternating current batteries?" inquired Erg.

"Well, it is time that we learned about the nature of batteries," said
I, "if you boys are going to have two storage batteries to care for."




XIV

DOING CHORES BY ELECTRICITY


Chores were my salvation in youth, and those chores were not trifles. I
was made to feel that the whole family depended on my milking the cows,
bringing in the eggs, keeping the wood box full of wood, the water pail
full of water brought from the old well, churning the butter, feeding
and watering the animals, and performing a multitude of regular daily
and weekly tasks. As I grew older my responsibilities were allowed
to increase proportionally so that I might feel some measure of the
dignity of being a mainstay and a support of the family. Long before I
reached manhood occasional opportunities were presented for me to play
the full part of a man. These sometimes came during a temporary absence
or sickness of my father, but more often, as I learned afterward, by
his skilfully eliminating himself from the situation so that I might
try my powers.

We attempt in the present generation to furnish a substitute for the
old time chores by our daily programme in school or in summer camp,
but I often wonder whether this round of trifles can make men. Can one
grow great without having a chance to feel occasionally that the world
depends upon what he does?

[Illustration: Fig. 143]

The great advantage of Millville to us all lies in the fact that my
wife is a good organizer. She immediately saw that the introduction
of electricity into the cottage enabled her to assign chores to us
all. These chores were assigned so that the establishment ran like
clock-work. On Monday morning in a large room, called the wash room,
she arranged the soiled clothes in five piles. Pile No. 1 contained
sheets and pillow cases; No. 2, white shirts, shirtwaists, and other
starched clothes; No. 3, underclothes; No. 4, towels, etc., and No. 5,
coloured clothes. Here stood a washing machine run by electric motor
and a wringer run by the same motor (Fig. 143). By the side of it sat
a tub for rinsing water and next to that a tub for bluing water. Two
boys placed a wash boiler over a two-burner oil stove, put five pails
of water into it, and cut up one cake of laundry soap which they also
put in. When this was boiling hot, about half of it was poured into the
washing machine. The other half was to take its place later in the
washing machine. The first pile of clothes was put in and the motor
run for five minutes. This batch was then run through the wringer into
the rinsing water, and then again through the wringer into the bluing
water, and then through the wringer a third time into the clothes
basket, and hung upon the line out doors in the clear sunshine, which
did more than all else to make them sweet and clean. A basket of such
clothes from the line makes you want to plunge your face right into
it and take a good whiff. There is nothing like it except a mow full
of new hay. The piles of soiled clothes follow one another through
this series of tubs on about a fifteen to twenty minutes headway, so
that the whole family washing is done wholly by two boys inside of two
hours. Each pile after the first is given ten minutes in the washing
machine.

On Tuesday the ironing is done with electric irons (Fig. 144). On
Friday the house is cleaned by the vacuum cleaner, run by electricity
(Fig. 145).

[Illustration: Fig. 144]

[Illustration: Fig. 145]

On Saturday a lot of baking is done in a series of fireless cookers
(Fig. 146).

The sewing machine runs more than ever before. I hear "It is such fun
to sew with an electric motor." And the electric fan which Harold
installed for his mother over the sewing machine "makes that the
coolest spot in the house."

[Illustration: Fig. 146]

[Illustration: Fig. 147]

Chores do not take all of the time, nor most of the time. They
are simply the important things which must be done right on time.
Meanwhile there is plenty of time for other things and a vast lot of
experimenting goes on down at the mill. It is my chief entertainment to
stroll down there every day and look on. One day I found this project
on trial: On the floor (Fig. 148, _f_) of the room over the wash room
at the mill a large dripping pan _A_, was set on blocks of wood so that
one corner was lower than the rest. A rubber pipe, _B_, brought water
to this pan from the mill pond, an inverted faucet, _c_, regulating the
flow. The overflow from the pan fell into a funnel, _d_, the stem of
which went through a hole in the floor. A short piece of rubber pipe
connected this with the nozzle, _e_, of a gardener's sprinkling can,
which hung from the ceiling in the compartment for the shower bath.
Electric lamps attached to a board, _g_, were inverted over the pan
of water, so that the bulbs of the lamps were immersed in the water.
The electric current for these lamps was controlled by a switch, _h_,
placed by the side of the water faucet. When one wanted a shower he
could have it as cold or as hot as he chose by adjusting properly the
switch and the faucet. Moreover, it was not necessary for him to wait,
for warm water flowed immediately.

[Illustration: Fig. 148]

In discussing this the boys said that a 32-candle-power lamp used 110
watts, and that since 96 per cent. of the energy supplied to the lamps
went into heat each lamp transformed 105 watts of electrical energy
into heat. But 100 watts sufficed to raise one pint (one pound) of
water five degrees in one minute. They used seven lamps or about one
horse-power, and adjusted the flow so that the shower delivered one
quart of lake water per minute warmed for a tepid bath.

[Illustration: Fig. 149]

The next time I sauntered down to the mill the boys were working on
what they called an electric shower bath. They had fastened upon the
wall of the bath room an electric bell (Fig. 149), and placed on a
shelf near by a battery of two dry cells, _P_. The switch which closed
this primary circuit was on the wall by the side of the faucet and
electric heating switch (Fig. 148). One of the wires, _S_, for the
secondary circuit was carried up and connected to the pan _A_ (Fig.
148). The other wire was fastened to a sheet of zinc about a foot
square, which lay upon the floor of the shower bath. The idea was that
when one was taking a shower bath, if he chose to vary his sensations
he might step upon the sheet of zinc, close the switch in the primary
circuit and let the secondary current pass through his body by way of
the shower. They said that it was particularly prescribed for slow
people.

Speaking of chores, of course the most insistent chore was to keep the
storage batteries stored. This process gave rise to many questions,
through which the information contained in the next chapter was brought
out.




XV

ELECTRIC CURRENTS FROM CHEMICAL ACTION AND CHEMICAL ACTION FROM
ELECTRIC CURRENTS


Luigi Galvani (1737-1798) of Bologna, Italy, in 1786 unwittingly
produced an electric current from chemical action. Because he was
eagerly seeking other results he misinterpreted this. Several words in
the dictionary are becoming either obsolete or misnomers. For example,
galvanism is an old-fashioned word for an electric current. The
expression _galvanic electricity_ is a relic of the abandoned idea that
there are several kinds of electricity, of which Galvani discovered
one. Galvanized iron is wholly a misnomer. It is a name used for iron
which has been coated with zinc, and it suggests the idea that somehow
the zinc is coated upon the iron by means of an electric current,
whereas in fact it is done by dipping the iron into melted zinc.

Alessandro Volta (1745-1827) of Como, Italy, took up the discovery
of Galvani, interpreted it correctly, and perfected the method
of producing electricity by chemical action. What these two men
really discovered was that it is possible to produce continuous
currents of electricity. Before that electricity was known only by
the instantaneous discharge or spark. From the name of Volta is
derived the word volt, which designates the unit of electro-motive
force. The adjective _voltaic_ is synonymous with _galvanic_, as
voltaic or galvanic cell, voltaic or galvanic current. For a long
time it was thought that such an adjective was needed to designate
electric currents generated by chemical action as a peculiar kind of
electricity. We no longer think of electricity which is generated by
chemical action as different from that generated by a dynamo or from
any other source.

For about seventy-five years after the discovery of Galvani chemical
action was our only method of generating currents of electricity, and
it is largely owing to the inadequacy of this method of production that
so few uses for electricity were discovered previous to the perfection
of the dynamo about a third of a century ago. Two things have conspired
to bring about this _age of electricity_. (1) The dynamo reduced the
cost of production from five dollars to ten cents per kilowatt hour.
(2) Mankind grew extravagant, greatly increased the number of things
which it considered necessary, and at length became both able and
willing to spend more for the things which it demanded.

The so-called voltaic cell is of scarcely more than academic interest
now. The school which, as a rule, follows half a century behind
practical life, has taught and still teaches the philosophy of the
galvanic cell with great particularity. It is now being urged to
undertake the teaching of the dynamo. Meanwhile the dynamo has almost
driven out of existence all electric battery cells except the storage
cell and the so-called "dry cell," and each year the dynamo is
encroaching more and more upon the territory of the dry cell. In the
present day, when a passenger upon a street car pushes a button to stop
the car, he uses, not a voltaic cell, but a 500-volt dynamo current to
ring a small buzzer, and it costs the company not one-hundredth part
as much as it would to furnish him a battery equipment to do the same
thing. Small dynamos and magnetos are displacing dry battery cells in
the sparking equipment of motor boats and automobiles.

We lifted a dry battery cell out of its pasteboard case and found that
it was contained in a metal cup of sheet zinc. The top of this was
sealed over airtight with pitch, the purpose of which is to prevent
this "dry" cell from drying up. We dug away the hardened pitch and
found a black powder which was distinctly moist. In case the pitch
becomes cracked or a hole appears in the zinc cup, the moisture passes
out and the cell ceases to act as a generator of electric current.

The zinc cup had a lining of pasteboard on the sides and the bottom,
similar to the pasteboard which enveloped the outside, only the lining
was quite moist. A corrugated rod of carbon about an inch in diameter
occupied the middle of the cup, and the space around it was packed
full of a mixture of ammonium chloride, manganese dioxide, and other
substances like plaster, etc., which differ with different cells. A dry
cell which has been long in use is quite apt to show stains upon its
pasteboard case. These are caused by holes which appear in the zinc.
The production of electric current by the cell is dependent wholly upon
a chemical action between the zinc and the ammonium chloride which
results in the destruction of both. This chemical action cannot go on
without moisture.

The zinc cup of the particular cell which we were examining appeared
to be intact, and we proceeded to dig out the black powder. Its black
colour is due to the manganese dioxide. Ammonium chloride is white.
We lifted out the carbon rod and scraped the zinc cup clean. The
binding posts attached to both the zinc cup and the carbon rod were
left intact. Into the zinc cup we now poured a tumblerful of water
and added about a quarter of its volume of hydrochloric acid, setting
the whole into a large bowl to guard against disaster. Bubbles of gas
were formed rapidly, causing the liquid to effervesce as a tumbler of
soda water would do. We inverted an empty tumbler over the cup so as
to collect this gas. In about two minutes we lifted the tumbler, still
holding its mouth downward, and brought a lighted match to it. There
was a flash and the contents burned with a pale-blue flame. Some of
the zinc had united with some of the hydrochloric acid and set free
hydrogen gas, which is one of the constituents of the acid. This is
typical of chemical actions. Something similar takes place between the
ammonium chloride and the zinc. Three interesting things occur in this
experiment:

1. Chemical action, just described, is produced.

2. Heat is produced. This was very evident when we took the zinc cup up
in our hands. It was as hot as though boiling water had been put into
it.

3. An electro-motive force is produced. This we showed by connecting
one end of a piece of copper wire to the binding post of the zinc cup
and the other end of the wire to an electric bell. Another wire ran
from the bell to the carbon rod. When the carbon rod was lowered into
the acid the bell rang.

Within ten minutes holes began to appear in the side of the zinc cup.
The acid contents began to flow out into the bowl, and not long after
the zinc fell to pieces. After fifteen or twenty minutes the action
began to grow less. The acid was being used up as well as the zinc. If
enough acid is added the zinc will wholly disappear.

We have chosen substances which would produce striking results in this
experiment, but the same sort of thing is going on about us continually.

One summer by the seashore I fastened a brass plate upon my boat with
two screws--one of brass and one of galvanized iron. The plate was
attached below the water line so that it might be acted upon by the
salt water. Within three weeks the head of the galvanized iron screw
had entirely dissolved, while the brass screw was as good as ever. A
galvanized iron screw near by but not in contact with the brass was
still in as good order as ever. I had simply made an electric battery
cell out of the ocean by dipping into it zinc and brass in contact.

A most interesting relationship exists between the three kinds of
activity in the cell, which have been mentioned, viz.: (1) chemical
action; (2) production of heat; (3) production of electric current.

As has been already noted, chemical action produces heat. Conversely,
if we apply heat to the cell we greatly increase its chemical action.
We have also noted that chemical action produces an electric current,
but unless the current is allowed to flow through some external channel
like a closed circuit of wire the chemical action is greatly restrained
or entirely checked.

[Illustration: Fig. 150]

In a glass tumbler I put a rod of pure zinc (Fig. 150, _Zn_), and
an electric light carbon, _C_. A short wire, _a_, was arranged for
connecting the two externally. In the tumbler was put some water with
about one tenth its volume of sulphuric acid. No chemical action was
evident until the wire was touched to the zinc, closing the circuit.
Then bubbles of hydrogen gas gathered upon the surface of the carbon
rod, and clung to it very tenaciously. We lifted out the carbon rod and
rinsed off the bubbles in another tumbler of water, and then returned
the carbon to its place in the cell. The experiment was repeated many
times, and each time no bubbles of hydrogen, which is in this case the
sign of the chemical action, appeared until the circuit was closed for
the flow of the electric current. Incidentally it should be said that
the amount of hydrogen produced by the chemical action is a measure
of the amount of electric current produced. Incidentally also it
should be said that the bubbles of hydrogen clinging to the carbon rod
check and almost stop both the chemical action and the production of
electric current when the circuit is closed. If now we put in sodium
bichromate to use up the hydrogen as fast as it is produced we may have
a continuous current whenever the circuit is closed. Chemical action
does not entirely cease in this cell when the circuit is opened. But if
two cells are prepared, and one is left with its circuit closed while
the other remains with its circuit open, it will be found that the zinc
disappears and the acid is used up in the closed cell in a short time,
while these remain not greatly changed for a long time in the cell on
which the circuit is open. No cell will remain forever without chemical
action, yet a dry cell which might use up its zinc and ammonium
chloride in a few hours if the circuit is closed may be kept idle
three or four years, and still be able to furnish electricity enough to
ring a bell. Some persons feel defrauded if the author of a book fails
to give them all the new words and conventional terms which belong to
any subject. For such here is a page or so.

It is conventional to speak of the electric current as flowing from the
carbon through the wire to the zinc, although every one has suspicions
that it may flow in the other direction or even that it may not flow
at all. It is conventional to designate any part of the circuit from
which the current comes as positive (+) to any other part toward
which it flows, this latter being considered negative to the former
and designated (-). The current is conceived of as making a complete
circuit, from carbon to zinc through the wire and from zinc to carbon
through the liquid. Hence, the binding post of the carbon rod is called
the + pole and that of the zinc is called the-pole, while the zinc rod
or plate beneath the surface of the fluid is called the + plate and
the carbon is called the-plate. The liquid is termed the electrolyte.
The sodium bichromate, introduced to cause the hydrogen to unite with
oxygen, is called an oxidizing agent or even a _depolarizing_ agent,
and hydrogen collecting upon the negative plate is said to polarize
the cell.

Hydrogen may be made to collect upon the carbon or negative plate until
the electric current reverses its direction. The hydrogen is said to be
more - than the zinc. If we connect the zinc and carbon rods with the
wires bringing an electric current from the dynamo we may make either
one positive as we choose, according to which is connected with the
positive wire. Hydrogen bubbles will collect upon whichever plate we
make the negative one.

When we send an electric current from the dynamo into this cell it
is called an electrolytic cell, and when it is used to generate an
electric current it is called a battery cell. In either case the
electrolyte is decomposed and put through a chemical change, though the
chemical action in one case is the reverse of that in the other, and
the direction of the electric current in one case is the reverse of
that in the other. For example let us consider the case of a zinc rod
and a carbon rod immersed in sulphuric acid and the external circuit
closed. The current passes as indicated by the arrows in Fig. 151, and
the chemical actions result in hydrogen leaving the sulphuric acid and
zinc taking its place, forming zinc sulphate. This is a white salt and
for purposes of this experiment must remain dissolved in water. So far
we have been considering a generator of electricity--a battery cell. We
may introduce something at _m_, say a motor, which will indicate that
an electric current is flowing. At length the cell ceases to generate
current and is, as we say, "run down." Suppose now we substitute a
dynamo in place of the motor in this circuit, connecting it so that the
carbon rod shall be its positive pole and the zinc its negative pole.
We now call this an electrolytic cell, (Fig. 152). The current will
decompose the zinc sulphate. The zinc will be coated upon the zinc rod
and hydrogen will be procured from the water present, of which it is a
constituent, to form again sulphuric acid as originally.

[Illustration: Fig. 151]

[Illustration: Fig. 152]

We shall thus restore the conditions which prevailed in the first case
as represented in Fig. 151. H_{2}SO_{4} is the chemist's designation
of sulphuric acid and ZnSO_{4} is his expression for zinc sulphate.

The experiment illustrates a storage battery so called. It might better
be called a chemical transformer.

It is wholly unnecessary that one rod be composed of zinc. If we
begin with both rods of carbon immersed in a solution of ZnSO_{4},
and send into this cell the dynamo current, the carbon which acts as
the negative pole will be coated with zinc in a short time, and we
shall have in effect a rod of zinc and one of carbon as before. After
a minute or two we may disconnect the generator and substitute in its
place a bell as indicator, and it will ring, showing that we have
transformed electrical energy into chemical energy which is now being
retransformed into electrical energy. We say that we store electricity
by this means, which is, however, no more true than that a farmer
stores his farm in the bank when he sells it and deposits the money
until he shall need it to buy another farm.

Here is a very beautiful blue salt. I will drop a few crystals of it
into a tumbler of water and dip in two carbon pencils connected to the
dynamo current, using between fifty and sixty ohms of resistance in
the circuit so as to have two amperes flowing. After a minute or two I
lift out the negative carbon and you see that it is well plated with
copper. The blue salt is copper sulphate. If we weigh the negative
carbon, both before and after the experiment, we shall find that copper
has been depositing at the rate of one ounce in twelve hours. If we
reduce the current one half, making it one ampere, it will deposit
copper at the rate of one ounce in twenty-four hours. One ampere will
separate three ounces of lead in a day from a solution of any lead
salt; it will separate .9 ounce of iron in a day from a solution of
any iron salt, and it will liberate from water, which is a compound of
hydrogen, one gallon of the gas in ten hours. The amount of chemical
action is a measure of the amount of electrical energy expended. Before
the present form of commercial wattmeter was devised electrolytic cells
were used to determine what the consumer's bill for electricity should
be each month. These chemical meters contained a solution of zinc
sulphate for the electrolyte and both the positive and the negative
plates were of zinc. While the current is passing, zinc from the
solution is coated upon the negative plate and zinc from the positive
plate takes its place in the solution, thus maintaining a constant
strength of solution.

Here are three iron nails. I propose that you plate one with zinc
and another with copper and then expose all three to the weather
and see which will rust. I propose that you replate all the spoons
at the cottage and the metal tops of the salt cellars with silver.
Electro-plating results better if done slowly. Ten volts and .1 ampere
will be sufficient current.

In the storage battery we generally use lead for both positive and
negative plates and dilute sulphuric acid for the electrolyte. Hydrogen
is liberated at the positive plate and oxygen unites with the negative
plate. When the charging current is cut off the chemical action
reverses, and an electric current is produced by the cell.

In all other batteries there is a destruction of one plate and of the
electrolyte, which cannot be fully restored by a charging current,
although in the case of the lead and sulphuric acid combination the
charging and discharging of the cell may go on alternately for a very
long period without permanent change or loss of any substance except
water. There is, however, plenty of loss of energy in this as in other
transformers. One hundred ampere hours of current expended to charge
a storage battery will yield from seventy-five to eighty-five ampere
hours while the battery is discharging.

The lead storage battery is, however, full of disappointments for
those who do not properly care for it. It is irretrievably ruined if
neglected and allowed to charge too far, or discharge too far, or
evaporate too much water, etc. The voltage of a lead cell must not rise
above 2.2 nor fall below 1.8. It must not be allowed to furnish at any
one time a greater number of amperes than it is rated for. It must
not stand idle too much. It must not be cleaned up and put away for a
period. In fact, the lead-sulphuric acid battery is so poorly adapted
to our need that I feel disposed to try Mr. Edison's new storage
battery. This has nickel hydrate packed in tubes of metallic nickel for
the positive plates and iron oxide pressed into pockets in a sheet of
metallic iron for the negative plate. A solution of potassium hydrate
in water is used for the electrolyte. This is said to be uninjured by
being emptied out and left idle, as our batteries must be for a large
part of the year. The e. m. f. of this battery is less than that of the
lead battery, being only 1.2 volts. We shall therefore need ninety-six
cells (type _B-4_) for the machine shop and ninety-one cells of the
same kind for the cottage. Our dynamo will be unable to charge at one
time more than sixty of these cells connected in series.

The particular chore which you boys must perform is to see that the
voltage of these batteries is maintained at about 1.2. It should
be charged up to 1.8 volt at least once a week and never allowed
to discharge to a lower pressure than one volt. The level of the
electrolyte must be maintained one half inch above the plate by adding
distilled water occasionally.

A few years ago every student of chemistry was more or less agitated
by the thought that more than half of every clay bank was composed
of metal nearly as valuable, or at least as costly, as gold. This
is aluminum. By all the methods then known it was a very difficult
and expensive process to extract the metal from the clay. At length,
by the perfecting of the dynamo, the chemist had under his control
great and powerful electric currents which enabled him to unlock any
chemical compound however refractory and isolate its elements. As a
result aluminum became common enough and cheap enough for even kitchen
utensils.

The metal calcium which a short time ago was an exceedingly rare
substance worth $40 an ounce is now fairly abundant and cheap for
chemical experiments, although it has no qualities which will give it
an extended use.

Powerful electric currents, such as are obtained at Niagara, enable us
to combine elements into hitherto unknown chemical compounds. Carbon
and silicon are made to unite to form carborundum, which vies with the
diamond for hardness. Carbon and calcium unite to form calcium carbide,
used with water to form acetylene gas.

In such processes the intense heat of the electric arc--perhaps 6000
degrees--is employed, together with the electrolytic action of the
current, to separate and combine substances. Enormous currents are used
in the electric furnaces for producing chemical reactions--from 1000 to
30,000 amperes at a time.

Electric currents passing through the human body expend their energy
partly in heat and partly in electrolysis. So simple and harmless a
thing as common salt would become a virulent poison if it could be
electrolized in the body into its elements _sodium_ and _chlorine_.

Let us make use of an electric current to decompose water into its
elements, hydrogen and oxygen. I have a three-ounce wide-mouthed
bottle (Fig. 153) and through its cork I pass two short pieces of No.
24 platinum wire by pushing a stout needle through first. I fill this
bottle with pure water and cut a slight furrow in the side of the
cork, where water may drip out when the gas is produced in the bottle.
We crowd the cork firmly into the mouth of the bottle and invert it.
No water drops out. We bend the ends of the platinum wires into hooks
and hang upon them the wires bringing the dynamo direct current. There
is no evidence of chemical action. Pure water is an exceedingly poor
conductor of electricity. Let us now put about fifty-five ohms of
resistance into the dynamo circuit, so that it will pass about two
amperes, and put a very small pinch of salt into the water, which makes
it so good a conductor that its resistance may be ignored. When now
we close the circuit, as before, a brisk effervescence takes place.
Bubbles of gas rapidly form on the platinum wires and break away,
rising through the liquid. Twice as many form on the negative wire as
on the positive one. As these gases rise to the top of the bottle an
equal volume of the water drips out through the small hole in the cork.

[Illustration: Fig. 153]

Two amperes of electricity will liberate two fluid ounces of hydrogen
at the negative pole and one fluid ounce of oxygen at the positive
pole, in five minutes. Hence in five minutes the bottle should be
full of a mixture of two gases, two thirds of which, by volume, is
hydrogen and one third oxygen. We will catch the water which drips out
so that we may measure it. The bottle being now full of gas I shut off
the current, and removing the cork I bring a flame to its mouth. A
very loud and startling explosion takes place. We pour the water back
into the bottle, and it seems to fill it as well as before. We have
decomposed a few drops of water--not enough to measure--into two gases,
one of which, the hydrogen, occupied two thirds of the bottle, and the
other, oxygen, occupied the remaining third. At ordinary temperatures
they would not reunite, but when raised to their kindling temperature
they united, producing light, heat, a loud noise, and the few drops of
water which had been originally decomposed by the current.

This is the electrolysis of water. I wonder if any such chemical action
took place in Ernest's body when he received that severe shock on the
motor boat the other day.

It is significant that the "dry" battery cell must be moist in order
that chemical action may go on in it. Compare with that fact several
others that we may learn from observation, for example: Baking powders
must be kept dry to retain their strength. That is, if they get moist
chemical action will begin in them, and the gas which is one of the
products of this chemical action will pass off. Now it is the sole
function of baking powders to produce gas within the dough, and if the
gas has wholly or partially escaped they will fail to make the bread
stuff "light." The same reasons obtain for keeping seidlitz powders and
other effervescing salts, such as vichy and kissingen, dry. It is to
prevent the chemical action which is provoked by the presence of water.
The same thing is true of the rusting of iron, and the various kinds
of corrosion of metals. We may prevent such action indefinitely by
keeping them dry. Berries, fruits, meats, milk, eggs, grain--all kinds
of foods--are preserved from spoiling--from chemical changes--by drying
them and keeping them dry. The same thing is true of wood, paper,
cloth, etc. A wooden fence post may last from five to ten years. A
fence rail, being less exposed to moisture, may last two or three times
as long. The interior wood of a house may last a century or two, while
the exterior wood, being exposed to the weather, may require repairs
very frequently. Shingles on the roof do not last as long as shingles
on the side of the house. Those on a steep roof last longer than those
on a flatter one. A pitch of at least forty-five degrees in a roof is
desirable to keep it dry. The north and west sides of a house being
least exposed to storm in this climate last the longer. Precious books,
records, deeds, wills, etc., on paper must be preserved in dry air. A
sail will keep strong and white if kept dry.

But it is impressed upon us by our experiences that sunlight is even
more potent than moisture to produce chemical change. Photographic
processes are dependent upon the power of light to produce chemical
changes. The fading of our tapestries and our garments, the tanning of
our skins, the development of green material in the leaves of plants,
all are evidently the direct result of sunlight. A picture hung on
the wall prevents the wall paper behind it from being faded by the
light, or it prevents the wood behind it from being turned yellow by
the light. Folds in our garments prevent them from being faded all
alike. Very many substances to be found in a chemical laboratory, in
a drug store, or in a kitchen must be kept in the dark if they are to
be guarded against chemical change. No experienced housewife would let
a barrel of flour or potatoes sit in the sun, and every housewife
knows that the sun is the best agent for bringing about those chemical
changes which she desires. Hence she puts her bedding, her milk pans,
her bread box, her butter jar, etc., "out to sun." She has open
plumbing, that the sun may enter those dark and dirty corners.

If you would guard a substance against chemical change, keep it in a
dry, dark place. We have come to associate the sun and the weather as
disintegrating forces. Hence the south and east sides of the building
need most frequent repairs. Every one who has made time exposures in
photography knows that the sunlight from the east is, as a rule, two or
three times as powerful as that from the west. There is less moisture
and dust in the air to screen us from the early morning sun than from
the late afternoon sun. When there is enough moisture in the air to
make the sun look red, those rays from it which would produce chemical
action, called actinic rays, are cut off. Photographic processes are
then exceedingly slow. It is like exposing a plate in a dark room
behind the ruby glass.

But our daily experiences teach us that not only moisture and light but
also heat stimulates chemical action. We restrain chemical action by
cold when we put things in the ice box. We hasten chemical action by
heat when we put things on the stove. Winter restrains all the chemical
activities of nature, and summer quickens all the vegetable and mineral
kingdoms into chemical activity. If we would preserve a substance from
chemical change we must keep it in a _cool, dark, dry_ place. Now
those conditions which will favour the chemical activity of a battery
cell will enable it to produce electricity, and those conditions which
will restrain chemical action will enable us to preserve the cell from
running down.

But we have lately learned that other forms of radiation besides
light and heat exist and aid in chemical action. We may produce
radiographs--pictures on photographic plates--without light but with
invisible rays, which are akin to light and to electricity.




XVI

ELECTROCUTION AT MILLVILLE


The old mill was infested with rats. My wife laid down to the boys
the principle that good housekeepers were never troubled with vermin
of any kind. The rats' sole occupation is to search for food. If you
don't feed them they will not stay with you. But the boys said that
they were glad of a chance to try an experiment on the rats. So one day
when I went down to the mill I found them discussing the possibility of
killing the rats by electricity. Harold said that he had read that it
took much less electricity to kill any animal than to kill a man, and
he would like to try, for instance, whether the shock which they had
received from a bell would kill a rat.

"Well, who's going to sit by," said Erg, "to close the primary circuit
when the rat happens to get himself into the secondary circuit?"

"Make him close it himself by some device," said Ernest.

"They have a regular thoroughfare, a beaten highway, along by the
wall, under the mill and up through a hole in the floor of my bedroom,"
said Dyne.

[Illustration: Fig. 154]

[Illustration: Fig. 155]

"Well," said Harold, "I propose an electric trap which shall have two
compartments. We will keep cheese in the inner compartment, the walls
of which shall be of wires so that the rats may see the cheese. The
floor of the outer apartment shall be covered with wire, as shown in
Fig. 154. The wires of the secondary circuit from the bell (Fig. 156)
shall be fastened to the binding posts _b_ and _c_ (Fig. 154). The
partition _d_ shall be a swing door into the apartment _A_ where the
cheese is. This is shown in profile in Fig. 155. _d_ must act as a
switch to close the primary circuit through the bell _P_ (Fig. 156).
We will have three dry cells in the primary circuit. Now this is the
way it will work: A rat comes up from under the mill with wet and
slimy feet--just suited for making contact for the electric current
to enter his body. The smell of the cheese attracts him. He circles
around the trap several times, watching the cheese in apartment _A_
through the wire screen. He sees a narrow opening into this apartment
under the door _d_. He puts himself in position upon the floor of
the outer apartment _B_, his feet bridging the gaps between the two
systems of wires belonging to the secondary circuit. When he thrusts
his head under the door and pushes it, it swings in a little, bringing
one metal strip against another, which belongs to the primary circuit.
This closes that circuit. He will never hear the bell ring, for the
electric current which will shock him to death travels 186,000 miles
per second, while his sensations travel only sixty miles an hour. If
the involuntary recoil of his muscles does not make him jump back, so
that the door will shut and stop the bell from ringing, Dyne will be
awakened and he will close the door, since we will put the trap at that
hole where the rats enter his bedroom."

[Illustration: Fig. 156]

The next night three rats were electrocuted by this device.

I told the boys they had so many interesting things going on at the
mill that we should have to have a telephone between it and the cottage
so that we could talk them over.




XVII

THE TELEPHONE


The telephone was the great invention of our centennial year, 1876.
Elisha Gray and Alexander Graham Bell each claimed to have been the
inventor. It is quite probable that each did discover it independently,
but the result of the long patent suit was that the court awarded the
claim to Bell. It is, therefore, known as the Bell telephone.

Many who installed telephones during the first few years of their
existence had them taken out again as nuisances. They are far greater
nuisances now than at that time, but the necessity of them has come
upon us and entirely enslaved us.

There were more than eleven billion messages sent by telephone in the
United States in 1907. The capital invested in telephone business was
$814,616,004. The income for that year was $184,461,747. All of these
items had more than doubled during the previous five years. In 1880
there were about eight times as many miles of telegraph wires as of
telephone wires. In 1907, there were about eight times as many miles of
telephone wires as of telegraph wires. The Bell system had 3,132,063
stations, and independent companies had 2,986,515 stations in 1907.

The first telephone line ran from Salem to Boston, Mass. This was in
1877. The next year the first telephone exchange was established. It
was eight years before a telephone line was extended from Boston to New
York. On October 18, 1892, the first telephone message was sent from
New York to Chicago. Previous to 1895 telephoning, like telegraphing,
was done by one wire, using the earth, as we say, to complete the
circuit.

But at about that time electric car and electric lighting lines became
so common that they interfered with telephoning. These currents running
in lines parallel to the telephone wires induced currents in them, and
when a person put a receiver to his ear for conversation he heard the
hum of electric light dynamos and the buzz of electric cars so loud
that conversation was quite impossible. The next step was to introduce
a return wire--the double metallic circuit as we call it. Thus outside
currents induce equal and opposite currents in the two wires of the
circuit, which neutralize each other.

It was this same year, 1895, that the "central battery" system was
introduced into telephone equipment. This is not usually a battery at
all, but a dynamo.

The price of all electrical supplies in 1895 was about one tenth what
it had been in 1885, and at the same time the goods were of far better
quality.

Important telephone patents expired in this year, and immediately
private and independent lines began to be established. It was also in
1895 that the telephone company began to use an automatic registering
device which enabled it to charge telephone rates according to the
number of calls.

The boys unscrewed the end of a telephone receiver (Fig. 157) and found
inside a permanent magnet made of several steel bars bolted together
(Fig. 158). This was shown to be a magnet by presenting a small pocket
compass to either end. The left-hand end of this magnet proved to be
its north pole by repelling the blue end of the compass needle.

[Illustration: Fig. 157]

[Illustration: Fig. 158]

[Illustration: Fig. 159]

On the left-hand end of the magnet was a small spool of No. 36 copper
wire, silk covered. It offered 75 ohms of resistance, and since it
takes 2-1/2 feet of this wire to furnish 1 ohm of resistance the spool
contains 187-1/2 feet. A thin disc of soft iron .01 inch in thickness
is held by the hard rubber case very near to but not quite touching
this end of the magnet. We drew this disc to one side, as shown in
Fig. 159, and connected the receiver by wires to a magneto. We turned
the crank of the magneto slowly and the iron disk danced up and
down, keeping time with the revolutions of the armature. The magneto
furnished an alternating current, which, when it flowed around the
coil in one direction, strengthened the pole of the magnet, and in the
reverse direction weakened the pole. When the crank was turned so as
to produce twenty to thirty revolutions of the armature per second the
dancing of the disc sounded like the low hum produced by the wing of
a humming bird. When a large, wide-mouthed bottle was brought near to
this the sound was greatly reinforced, as the sound of a bee becomes
louder when he appears at your open window. We next replaced the iron
disc and put on the cap again. We then connected the receiver at _S_
(Fig. 160) and connected two dry cells at _p_. When the primary circuit
was closed the disc vibrated in time with the hammer of the bell making
the same tone. We substituted for the bell a series of buzzers. The
smallest had an armature about one inch long, while that of the largest
was about two inches long. The shorter the armature the faster it
vibrated, and the higher was the pitch of its tone. We arranged these
as shown in Fig. 161. _A_, _C_, _D_, _E_ and _F_ are the buzzers. _B_
is a battery of two cells and _G_, _H_, _I_, _J_ and _K_ are springs of
sheet brass which act as push buttons. By operating upon these springs
with one's fingers, as upon the keys of an organ, it was possible to
represent the tones of a reed organ after a fashion. The armatures are
reeds and they are made to vibrate by electro-magnets. We called it
an electric organ. The telephone receiver was connected at _T_, and
the wires which led to it were lengthened so that the receiver might
be a long distance away. The disc in the receiver kept time with the
armature of each buzzer when it sounded and faithfully reproduced its
sound. But the strangest thing was that when any two buzzers sounded
together, or, indeed, if all five buzzers sounded together, the
receiver responded to them all at the same time, so that a person in
another room or in another house, with the receiver at his ear, might
hear exactly what those did who were in the same room with the buzzers.
The wires from the receiver were connected with the coil in each buzzer
so as to get the induced current, as shown in detail in Fig. 160.

[Illustration: Fig. 160]

[Illustration: Fig. 161]

[Illustration: Fig. 162]

We took a telephone induction coil (Fig. 162) and fastened it to a
board as represented in Fig. 163, _I_. One wire of the primary circuit
was fastened to the binding post _a_. The other wire from the primary
coil passed to the switch _S_ and then to the battery. From the battery
the wire ran to the binding post _b_. _C_ is a steel tuning fork. The
secondary circuit is closed through a telephone receiver. These wires
are extended so that the receiver is too far distant for the tuning
fork to be heard through the air. When the switch _S_ is closed the
tuning fork acts as the interrupter for the primary circuit, and it
interrupts according to its time of vibration. If, for instance, the
fork gives the tone of middle _C_ on the piano it vibrates 256 times
a second. It interrupts the primary circuit 256 times a second. It
induces an alternating current of the same frequency in the secondary
circuit. The diaphragm of the telephone receiver vibrates in perfect
time with the tuning fork and produces the same tone as the tuning
fork. We had a series of tuning forks giving a variety of tones,
which we could substitute one after another in place of this one. The
receiver reproduced accurately the tone of each one of them.

[Illustration: Fig. 163]

[Illustration: Fig. 164]

We took a small induction coil (Fig. 164) _c_ and fastened one end of
the primary circuit to a battery, _B_. The wire at the other end of
the primary circuit was bent into a hook _h_. This hook was adjusted
about a quarter of an inch from the end of the iron core of the coil.
The other wire from the battery was attached to the steel strings of a
piano, _P_. When the coil _c_ was brought over a string and the hook
_h_ was allowed to pass beneath the string and touch it very gently,
the primary circuit was closed through the string, which served as an
interrupter of the current and vibrated according to its tone. The
secondary coil, not represented in the figure, was connected to a
distant telephone receiver, which reproduced the tones of the piano
strings.

Producing a tone is merely a matter of making something vibrate with
the required frequency. It may be a piano string, or a tuning fork,
or a reed of an electric buzzer, or the diaphragm of a telephone
receiver. If it vibrates 256 times a second, it will produce the
same tone as middle _C_ on a piano; if it vibrates 512 times a second
it will produce the _C_ which is an octave above, and if 128 times
a second an octave below middle _C_. The human voice is produced by
vocal cords in the throat, which vibrate with the proper frequency to
give any required tone. But how can we make the human voice act as an
interrupter of the primary circuit? An examination of the telephone
transmitter will supply the answer to this question.

[Illustration: Fig. 165]

[Illustration: Fig. 166]

The boys after taking the transmitter (Fig. 165) apart proceeded to
make one which should answer the purpose as follows: A block of wood
about one inch thick and three inches square (Fig. 166), _A_, was
hollowed out, making a cone-shaped cavity about one half inch deep and
one inch broad. This cavity was filled with small pieces of graphite,
_G_, made by cutting up a lead pencil. An old tin-type, _D_, was laid
over this as a diaphragm and tacked around the edges. A binding post,
_E_, passed through the block, its head being buried in the graphite at
the bottom of the cavity. The binding post _F_ furnished contact with
the tin-type. One dry cell was placed at _B_ and the sensitive ammeter
was connected at _C_. The needle showed that although a small current
was passing it was constantly varying in strength. Tapping upon the
table, walking across the floor of the room, shouting, and particularly
whistling, caused variations in the conducting power of the graphite
and consequently variations in the current strength. This is precisely
the condition we wished to produce in the primary circuit.

[Illustration: Fig. 167]

We next substitute for the ammeter at _C_ the primary and secondary
coil of the telephone. In Fig. 167 _T_ is the transmitter, _B_ is a
battery of two dry cells, _P_ is the primary winding of the coils, and
_S_ is the secondary winding. To this a telephone receiver, _R_ is
connected by wires long enough to reach into another room. A person
holding the receiver at his ear could hear everything said or done in
the room where the transmitter was almost as plainly as though he were
present in the room.

[Illustration: Fig. 168]

Two such transmitters were made and the second one was placed in the
room where the receiver had been, while a second receiver was installed
near the first transmitter. The arrangement is shown in Fig. 168. _T_
is the transmitter at one end of the line and _T'_ the transmitter at
the other end. _B_ and _B'_ are the batteries at each end, _P_ and
_P'_ the primary coils, _S_ and _S'_ the secondary coils and _R_ and
_R'_ the receivers. With this arrangement two persons carried on a
conversation with perfect ease, holding the receivers to their ears,
presenting their mouths to the transmitters and speaking in moderate
tones. _H_ and _H'_ are hooks upon which the receivers are to be hung
when not in use. These hooks act as switches to open and close the
primary circuit. A spring normally pushes the hook upward and closes
the circuit, but while the receiver is hanging upon it the circuit is
open at this point. Thus the battery is saved from running down when
the telephone is not in use.

The wires were finally extended from the mill to the cottage and this
equipment was installed at each end.

It will be noticed that the secondary circuit includes two receivers
and two secondary coils besides the wire of the lines to offer
resistance.

The receivers offer 75 ohms of resistance each. The secondary coils
offer 250 ohms each and the line wires between the mill and the cottage
offer 100 ohms. This makes a total of 750 ohms for the secondary
circuit. But the rapid alternations which are induced in the secondary
circuit impede the electric current ten times as much as the resistance
already mentioned.

When considering alternating currents passing through coils of wire we
are obliged to take into account two kinds of resistance:

1. Ohmic resistance.

2. Impedance.

"You boys understand the resistance to the flow of the electric
current, which we have so often measured in ohms. But I want to show
you that there is another kind of resistance which alternating current
meets. Here is a coil containing 1000 feet of No. 20 copper wire. I
throw on to it, for only an instant, the 110-volt direct current, and
the ammeter reads 11 amperes, showing that it offers a resistance of
10 ohms to the direct current. I now throw on the alternating current,
and the ammeter shows only a small fraction of an ampere. The surging
of the current back and forth induces a counter electro-motive force,
in the successive layers of the coil, which we call _impedance_. In
the experiment which we have just performed _impedance_ is fifty
times as important a factor as ohmic resistance. Impedance depends
chiefly upon the frequency of alternation. The impedance in telephone
circuits is particularly large because of the extremely high frequency
of the alternations produced by the tones of the human voice, these
being usually not far from ten times as rapid as those of alternating
currents in common use.

"We may estimate the total resistance of our telephone circuit as
equivalent to 7500 ohms.

"Our secondary coils have forty times as many turns as the primary
coils, and by means of them the voltage is stepped up to somewhere
near one hundred on open circuit. When closed through the line,
however, the voltage drops down to about ten. The result is that the
actual current which passes between the cottage and the mill when we
telephone is not far from .001 ampere. We may, however, hear a whisper
transmitted by .000001 ampere or less.

"The tone _E´_ which is produced by the tenth key above middle _C_ on
the piano, is the one most readily heard over the telephone. It is
produced by anything which vibrates 640 times per second."

[Illustration: Fig. 169]

We used No. 12 galvanized iron wire for our telephone lines. Two miles
of No. 12 copper wire would offer 16 ohms of resistance. The iron wire
offers about 100 ohms. But this is a trifle when compared with the
total resistance. We used a double metallic circuit so as to avoid the
effects of inductance from our electric lighting circuit.

[Illustration: Fig. 170]

The next thing that we were obliged to consider was some arrangement
for calling persons to the telephone for conversation. We decided
to use magnetos and alternating current bells. Fig. 169 shows the
essential mechanism of the bells. The bell at each end of the line
consists of two gongs _a, b_ and _a´ b´_, with a hammer _c_, _c´_
between them. This hammer is attached to an iron armature _h_, _h´_,
pivoted over the electro-magnets, _m_, _m´_, in such a way that it
rocks back and forth when an alternating current passes through the
lines _d e_, _f g_. The bells at both ends of the line always ring
together, since they are connected in series. A magneto (Fig. 170)
is situated at each end of the line. This, as has been previously
explained, is a generator of electricity, in which the field is
furnished by steel magnet, _M_. The armature _A_ is a coil of wire
whose ends are in contact with the leading out wires _d_ and _c_ by
means of brushes which slide upon rings. The armature is revolved by
hand. The crank and cog wheels employed to produce high speed are not
shown in the figure. By turning the armature rapidly this magneto will
develop 60 volts e. m. f. on open circuit. The magnets of the bells are
wound with a very large number of turns of very fine wire, so that
.025 ampere is sufficient to ring them.

[Illustration: Fig. 171]

Figure 171 shows how the magneto at either end of the line is
introduced into the circuit for the purpose of ringing the bells. _B_
and _B'_ represent the bells, _m_ and _m'_ the magnetos, and _P_ and
_P'_ represent switches. Springs push them upward so that they normally
close the circuit through the bells. When a person at _P_ wishes to
call another at _P'_ he pushes the switch _P_ down so as to bring his
magneto _m_ into series with the bells. When now he turns the crank and
generates the electric current, both bells ring. His own bell serves
the purpose of telling him that the line is operating all right. The
other bell calls the party desired for conversation. As soon as the
operator removes his finger from the switch _P_ the spring throws it
upward again, leaving his bell in circuit, so that he may be called
at any time, but cutting out of the circuit his magneto, which would
introduce unnecessary resistance.

The same wires which carried the current for ringing the telephone
bells carried also the current for operating the telephone receiver.
When the receiver is removed from the hook it releases a twofold
switch. This serves the double purpose of closing the primary circuit
through the local battery and substituting the telephone receiver
circuit for the bell-ringing circuit upon the line.

We used fifty chestnut poles to carry our line between the mill and the
cottage. Each pole had a cross bar, on one end of which the electric
light and power wires were carried and on the other end the telephone
wires. Glass insulators prevented the wires from coming in contact
with the wood of the cross bars. The necessity for this was impressed
upon the boys by something which happened while they were stringing
the wires. The telephone apparatus at the mill had been installed and
the two leading out wires had been connected to it. One of these was
coiled up on the floor, while the other had been strung along upon the
poles for half a mile, but had not yet been attached to the insulators
on the poles. While the boys were lunching at the mill, one of them
gave the crank of the magneto a turn, when, to the astonishment of all,
the bell rang. The circuit had been completed through the damp wood of
the mill, through the damp wood of some of the poles, and through the
earth. After lunch the wire, so far as it had been strung, was fastened
to the insulators upon the poles. But when some one turned the crank of
the magneto the bell still rang. We walked along the line to see where
the difficulty was. We found the end of the line about half a mile from
the mill dangling free from the ground, but touching a tall spear of
grass. When this was moved away from the spear of grass the magneto
could no longer ring the bell. The slight current required to ring
this bell--.025 ampere--had found its way through the spear of grass,
through the woodwork of the mill and through the earth.

We had no sooner got the two telephone wires properly strung and
attached to the hundred glass insulators when a thunder storm came up,
and drove us back to the mill for shelter. Pretty soon the bell rang
and we, supposing that some one at the cottage was trying to call,
went to the instrument, but could get no response, nor could we make
the bell ring. Lightning had sent an alternating current over the line
which rang the bell, but the strength of the current was too great for
our coils of fine wire and one of them was burned out, as we say. In
other words, the wire had melted at the point where it offered the
greatest resistance.

The burned-out coil was replaced, and then we installed lightning
arresters which were of two kinds. The first were simply fuses which
were introduced into the line to protect it against any current too
large for the apparatus to carry, and the second was a plate, _c_ (Fig.
172). These are to be found upon the top of the magneto cases. A wire
is connected with _c_, and its other end is grounded by being connected
with a piece of iron pipe which is driven deep into moist earth.

[Illustration: Fig. 172]

The plate _a b_ is inserted in the line, and the gap between this
and the plate _c_ offers sufficient resistance so that the telephone
circuit suffers no leakage at this point, but lightning has such
extremely high tension that it readily passes across this gap and finds
its way to the earth without damaging the instruments.

We have already noticed that our alternating current dynamo, which
produces 60 vibrations per second in the telephone receiver, causes it
to give a tone very nearly like the _C_, which is two octaves below
middle _C_ upon the piano. _C_ requires 64 vibrations per second. We
may speed up our dynamo so as to make it yield a tone exactly like _C_
or even above it.

Dr. Cahill of Holyoke, Mass., has devised an organ in which alternating
current dynamos produce the necessary number of vibrations for each
tone. The name _telharmonium_ has been proposed for this organ. It
has a separate dynamo for each tone, each dynamo having a frequency
corresponding to the tone required of it. The dynamo, for instance,
which produces middle _C_ makes the electric currents surge back and
forth 256 times a second, and this causes the diaphragm of a telephone
receiver to vibrate 256 times a second, and this sends forth 256 air
waves per second, and when these reach our ears we recognize the tone
we call middle _C_. The frequency of alternation in a dynamo may be
increased by either increasing its speed of revolution or by increasing
the number of coils upon its armature.

Mr. Cahill's great organ looks like a large machine shop with many
counter shafts geared so as to run at different speeds. On each shaft
are a large number of little dynamos whose armatures have various
numbers of coils. The organist, who may be far removed from this
"machine shop," fingers an ordinary keyboard. Each key opens and closes
a switch, thus bringing into action its own dynamo.

If the key which is known as _C_, one octave below middle _C_, is
pressed down, a switch closes the circuit between the telephone and a
dynamo which gives 128 double alternations of current.

The tone which is produced by 128 vibrations per second is the one most
often heard from a man's voice in ordinary conversation.

Another key brings into action upon the same telephone receiver--and
at the same time if desired--a dynamo which gives twice as many
alternations per second and produces the tone most often heard in
female conversation. It is middle _C_.

Another key might bring into action a dynamo which gives 64 vibrations
per second to the diaphragm of the telephone receiver. This would send
forth a tone very nearly like the base note of our 60-cycle alternating
current dynamo.

The following table shows a series of ten tones which might be produced
by the same little piece of sheet iron in a telephone receiver played
upon by ten dynamos at the same time. The whole list of ten tones would
sound well when produced simultaneously. The great mystery is that
the iron disc can vibrate in such a complex manner. It is important
to note, however, that the number of vibrations in each of the upper
tones is a multiple of that of the lowest tone:

    2nd octave above    C´´--1024   (= 16 × 64)
       Middle C         G´ -- 768   (= 12 × 64)
                        E´ -- 640   (= 10 × 64)[A]

    1st octave above    C´ -- 512   (=  8 × 64)
       Middle C         G  -- 384   (=  6 × 64)
                        E  -- 320   (=  5 × 64)

       Middle C         C  -- 256   (=  4 × 64)[B]

    1st octave below    G  -- 196   (=  3 × 64)
       Middle C         C, -- 128   (=  2 × 64)[C]

    2nd octave below    C,,--  64   (=  1 × 64)
       Middle C

    [C] The tone most easily reproduced by the vocal cords of a man.
    [B] The tone most easily reproduced by the vocal cords of a woman.
    [A] The tone which the telephone receiver responds to most readily.
    The table covers the range of the human voice, male and female.

All the intermediate tones, with their sharps and their flats, are
produced each by its own separate dynamo.

The insignificant amount of current required to operate a telephone
receiver makes it possible to furnish the music of these dynamos to
many and far distant telephones. This naturally suggests the idea
of having a great musician perform upon the keyboard and have many
auditors scattered about the city in their private homes or even in
many public halls, for the telephone receiver can readily be made
audible to a good-sized audience.




XVIII

ELECTRIC BELL OUTFIT FOR THE COTTAGE


The boys asked me what arrangement of electric bells we needed at the
cottage and so I gave them this problem to work out by themselves:

1. We want a bell in the kitchen to be rung by a push button at the
front door. But there are times when no one is in the kitchen and hence,

2. We want a bell upstairs to make a single stroke whenever the kitchen
bell is rung from the front door.

3. We want a floor push under the dining-room table which will cause
the kitchen bell to ring a single stroke.

4. We want a push button in the dining-room which will cause both bells
to clatter and call people from their beds, from the piazza, the lawn,
etc., to their meals.

This equipment needs only one battery of two dry cells, two bells,
three push buttons and about two hundred feet of wire. It should cost
less than five dollars.

The boys drew many plans and tried many schemes and at last determined
upon the plan shown in Fig. 173.

_P_ is the floor push under the dining-room table. When the circuit is
closed at this point the current leaves the battery from the carbon
pole _c_, passes up and around the magnets of the kitchen bell and back
to the zinc pole of the battery _z_ by way of the push button _P_. All
other circuits are open.

[Illustration: Fig. 173]

_P´_ is the push button at the front door. When the circuit is closed
at this point the current leaves the battery at _c_, passes up to the
right-hand binding post of the kitchen bell and divides, part going
through each bell. The portion of the current which goes through the
kitchen bell passes around the magnets and through the armature to the
left-hand binding post before it can find a path back to the battery.
Hence, the kitchen bell clatters. The portion of the current which
passes to the upper bell goes around its magnets and finds a path back
from the middle binding post to the battery by way of _P´_. Hence the
bell upstairs rings with a single stroke.

_P´´_ is a push button situated upon the wall by the side of the door
which leads from the dining-room to the kitchen. When the circuit is
closed at this point, the current leaves the battery at _c_, passes
up to the right-hand binding post of the kitchen bell and divides,
part of it going through each bell. The portion which goes through the
kitchen bell passes around its magnets and through its armature to the
left-hand binding post, then up to the middle binding post of the upper
bell, through its armature to its left-hand binding post and back to
the battery by way of the push button _P´´_. The other portion of the
current passes directly up to the right-hand binding post of the upper
bell, around its magnets, and through its armature to its left-hand
binding post, thence back to the battery by way of the push button
_P´´_. Hence, both bells clatter and keep time with each other. The
upper bell will ring independently of the lower bell, but the lower
bell is dependent upon the upper one to open and close its circuit,
somewhat as a relay.

Soon after the cottage had been equipped with electric bells I went to
the mill one day and found a push button at the door. Upon going in I
was curious to examine the electric bell outfit of that place and found
what is illustrated in Fig. 174.

[Illustration: Fig. 174]

A switch, _S_, had been attached to the bell. The boys said that when
they felt well they kept the switch upon the left-hand point and the
bell rang as a clatter bell. When they felt a little sick they put the
switch upon the middle point and the bell rang with a single stroke,
but when they felt very sick they put the switch upon the dead point
and the bell did not ring at all.




XIX

USING ELECTRICITY TO AID THE MEMORY


For the sparking equipment of the motor boat we use dry cells which
have an internal resistance of not more than .06 ohm. They will, when
short circuited through the ammeter for only an instant, give 25
amperes.

    (1.5 volt)/(.06 ohm) = 25 amperes

When we allow for a slight resistance in the ammeter itself, and for
the drop in voltage, we see that the internal resistance of a cell must
be even less than .06 ohm.

After being used about two months upon the motor boat these cells
develop more internal resistance, and they will then show not more than
six to ten amperes when short circuited through an ammeter. They are
then not reliable for ignition of the engine, but are quite as good as
ever for bell-ringing, and often continue so for more than a year. The
result is that we always have more partly run-down dry cells than we
can use. Seeing them about has stimulated the boys to devise ways for
using them.

The housekeeper is distracted by carrying on so many cooking processes
at one time. She forgets the eggs, and lets them boil five minutes
instead of three because the coffee must percolate twelve minutes, and
she lets the coffee percolate twenty instead of twelve minutes because
the biscuit must bake twenty minutes, and the biscuit are forgotten
because the pies must come out in thirty minutes, and the cake in
forty minutes. All this worries the cook. Harold is a sympathetic boy
and enters into the troubles of others. I had at one time shown him
how to bore a hole in a glass plate in five or ten minutes by using
a round file wet with water. One day he presented the kitchen with a
clock, intended to relieve the burdened memory of the cook. This is
represented in Fig. 175.

[Illustration: Fig. 175]

An ordinary kitchen clock had a hole bored through the glass which
covers its face. This glass is easily moved around in its metal rim,
bringing the hole over any desired minute upon the face. One wire
of the battery is attached to a leg of the clock, the other goes to
a bell, and then the wire from the bell is poked through this hole.
When the minute hand reaches that point the electric current is closed
through the metal of the clock, and the bell rings warning that the
eggs, coffee or what not are done.

We each urged that our memories should share in the vacation, and
applied for one of these outfits. I took one of the clocks and cut back
the minute hand so as to make it shorter than the hour hand, and then
had the hole in the glass made so that the hour hand should close the
electric circuit. This was kept at my study table and reminded me of my
appointments. Some used these clocks to alarm themselves in the morning
when they slept overtime.

Another reminder is shown in Fig. 176. _C_ is a float which rises and
falls with the water in our house tank. A cord running over two pulleys
connects this with a weight, _d_, hanging in front of a scale upon the
wall of the kitchen. This indicates how much water there is at any time
in the tank, which is situated in the garret. The boys arranged a bell
and battery so that when the tank is nearly empty the weight _d_ will
pull upward a spring, _a_, and make it close the circuit through the
bell to warn that water must be pumped. When the tank is nearly full
the weight _d_ pushes down the spring _b_ and rings the bell again.

[Illustration: Fig. 176]

Harold said that yeast cakes were the heaviest tax upon our memories.
If some one started for the village store, before he got out of
hearing, a call would come after him, "I forgot the yeast cake. Please
put that on the list." When one returned from the village store
with numerous packages, he would generally hear, "My yeast cake was
forgotten." We tried all sorts of schemes to get rid of this yeast-cake
nuisance, and finally adopted Harold's "curled bread" project.

We had built a brick oven out back of the house for experimental
purposes. Harold proposed that the boys bake a month's supply of bread
at a time, and, when it was a day or two old, cut it all into thin
slices and let it dry. These slices curled up as they dried and were
known as "curled bread." A flour barrel was filled with it each month.
It kept perfectly any length of time. The family voted it to be better
than crackers and better than fresh breadstuff of any kind.

Harold's suggestion regarding yeast cakes worked so well and was such
a relief to our memories that I proposed he next attack the problem of
the often forgotten salt in cooking.




XX

THE ELECTRIC BRICK OVEN


We had no end of experiments with brick ovens. One of the most
interesting was that wherein we used the brick fireplace as an oven
and did the family baking in it. On a cold morning we would build up a
smart wood fire in the fireplace and enjoy it during breakfast time.
Then we shovelled out the coals and the ashes, and shut it up tight
with a sheet iron arrangement and utilized the heat stored in the
bricks for doing all sorts of cooking.

Our outdoor brick oven and our monthly baking day were such a success
that they led to the construction of another oven of smaller dimensions
for the kitchen. This one was heated by electric lamps--one in each
of the eight corners. It had double glass doors in front so that the
cooking process might be watched. The glass of the inner door would be
clouded with moisture for a while, when the cooking first began, but
this would soon clear up, and then the lamps enabled us to watch the
colour changes in baking, etc. The lamps in the upper part of the oven
were connected with a different switch from those in the lower part of
the oven, so that we were able to control the browning on top or bottom
at pleasure.

Harold introduced a device for automatically controlling the
temperature of this oven.

[Illustration: Fig. 177]

Strips of brass and iron, _B_ and _I_ (Fig. 177), were riveted
together. These were fastened in the socket _A_. They are shown
edgewise in the diagram. The upper end of this compound strip is free
to bend back and forth in the plane of the paper, as here represented.
They normally touch the screw _C_. One of the electric light wires runs
from the lamps in the oven to this screw _C_. One wire of the dynamo
circuit _G_ goes to the lamps, and the other connects with _A_. Thus
the compound strip acts as a switch to open and close the circuit upon
the lamps.

This thermostat, as it is called, was placed inside of the oven.
Heat causes brass to expand more than iron and therefore when the
temperature reaches a certain height the thermostat curves, so as to
break the contact with _C_, and the lamps go out. When the temperature
falls a little the thermostat straightens until contact is again made
with _C_. _C_ is a screw and can be made to advance or recede in its
socket _E_, so that the temperature of the oven may be maintained at
any point desired. The wire of the screw _C_ extends to the outside of
the oven, where it carries an index, _D_, over the face of a dial, as
shown in Fig. 178.

[Illustration: Fig. 178]

The cook may set this index at any desired degree, and the lamps will
indicate when that degree has been reached. The thing to be baked is
then put inside and the clock, illustrated in Fig. 175, is set so as to
warn when the time is up.

The electric spark which occurs when the thermostat breaks contact with
_C_ causes the metals to corrode at that point, and corroded metals
are poor conductors. This corrosion is due to the oxygen of the air.
There is one metal--the expensive platinum--which is not corroded by
the electric spark. We drilled small holes in the end of the screw _C_
and in the brass strip and pounded into these holes little pieces of
platinum wire. Harold said he felt like a dentist filling a tooth. This
furnished good, clean contact at all times.

It takes a long time to heat up the brick oven, but it holds its heat
a long time and makes an excellent fireless cooker after the lamps are
turned out. It does not allow heat to escape into the kitchen, which
makes it a comfort in our summer cottage. We are all becoming daft on
_slowly cooked_ food--a sort of ripening process which gives time for
the chemical changes to take place and develops the finest flavours of
the food.




XXI

ELECTRIC WAVES


Much has been said about bringing young people up to do what they don't
like to do so as to make them strong and virtuous. My own life has
always been guided by a different principle. It is: _Find something
worth while which you will enjoy doing, and do it with your might._ I
am bringing up my boy on the same principle. In September we have a
real desire to get back to our work in the city, and in June we have
an eager longing for the occupations of Millville. I am not aware that
there is any part of my work which I would like to be relieved from,
and Harold and his mother said that they were now ready to return to
the city apartment with real pleasure for a winter.

One evening we were seated about the dinner table when Harold asked me
how electricity could travel without wires. I replied, "It travels as
light does. But I am very much puzzled to know why it ever follows a
wire when light does not." This did not settle the question and left
us both unsatisfied, so I told him to invite two or three of his best
friends in to-morrow evening, and I would perform some experiments for
them that would at least help them to think further upon this subject.

When the evening came I showed the boys an automobile spark coil to
which I had attached two knobs, _a_ and _b_ (Fig. 179), and with which
I had connected two dry battery cells. When I touch the wire _c_ to
the binding post _d_ a spark passes between the knobs _a_ and _b_.
When this spark occurs at least four kinds of waves pass out in all
directions from the spark gap between the knobs.

[Illustration: Fig. 179]

First, sound waves go through the air. Our ears detect these. If the
air is removed from around the apparatus no sound wave can go forth. A
careful examination of the internal ear shows us that it is constructed
so as to respond to such air waves.

Second, light waves go forth. These affect our eyes. We are blind to
the first kind of waves and deaf to the second. The light waves travel
without air--somewhat better without air than with air. A microscopic
examination of the eye indicates that it is constructed so as to
respond to waves. We believe there are waves in the ether which fills
all space. Sound waves travel in air at the rate of one mile in five
seconds. We had this nicely illustrated at the sea shore one summer.
The steamer touched each morning at a wharf which we could plainly
see two miles distant. We could see the steam arise when she blew the
warning whistle, and with our watches we found that it always required
ten seconds for the sound to reach us after we saw the steam of the
whistle. This at least showed us that it takes five seconds longer for
sound waves to travel a mile than it does for light waves to travel
the same distance. For light had to travel the same distance before we
could see the steam arise from the whistle. Although the time it takes
for light to travel a mile is inconceivably small, we have a simple
method of finding out that it requires eight minutes for light waves to
come to us from the sun.

The satellites of the planet Jupiter, in revolving about that body,
disappear and reappear at regular intervals, acting as flash lights to
mark time.

[Illustration: Fig. 180]

The earth, being 92,000,000 miles distant from the sun, is 184,000,000
miles farther from Jupiter when at _B_ than it is when at _A_. (See
Fig. 180.) It is found by observation that sixteen minutes more are
required for the light waves from a reappearing satellite to reach us
at _B_ than when we are at _A_. Hence eight minutes would be required
for light waves to travel the distance from the sun to the earth.
Although light travels at the inconceivable velocity of 186,000 miles
per second, the nearest star is so far distant that it takes light
three and a half years to come from it to us. The North star requires
forty-two years to send its light to us, and Arcturus is so far away
that waves of light sent out from it one hundred and sixty years ago
are only just reaching us now, and if it should cease to send forth
light now men would continue to see it for five generations yet to
come.

A third kind of wave which goes forth in the ether from the spark gap
of our coil is a heat wave. This affects neither our eyes nor our ears,
but I will undertake to make you conscious of it by another method.

[Illustration: Fig. 181]

Before a mixture of gasolene vapour and air can be ignited its
temperature must be raised to about 2000 degrees Fahrenheit. I will
show that heat waves pass out from this spark gap by placing my watch
crystal filled with gasolene underneath the knobs of the spark coil,
(Fig. 181). When now I close the electric circuit at the battery the
mixture of gasolene vapour and air just above the watch crystal is
ignited. If I increase the distance between the knobs you still hear
the crackle of the sound waves and see the light waves, but the mixture
of gasolene vapour and air does not ignite, because there are not heat
waves enough. The automobilist expresses this fact by saying a "fat"
spark or a "warm" spark is needed. A battery which has ceased to give
a sufficiently hot spark to explode the mixture of gasolene and air in
the cylinder of a gasolene engine may serve all other purposes quite
as well as ever. It may ring bells almost as long as it ever would.

I proved that the temperature for igniting a mixture of gasolene vapour
and air was nearly as high as melting iron, by heating an iron rod to a
dull red heat and bringing it to the watch crystal containing gasolene.
It did not take fire. I showed that it could not be ignited by a
lighted cigar, nor even by a glowing coal taken from the fire.

It was necessary to heat the iron rod to a very bright red heat--nearly
white heat, or nearly to its melting point, before it would ignite the
mixture.

These heat waves are ether waves, differing from light only in having
greater wave length. They travel at the speed of light, they travel
better without air than with air. They come from the sun and all other
light-giving bodies. Indeed, an ordinary incandescent electric lamp
gives out about twenty-four times as much energy in heat as in light.
Heat waves are being thrown off from all bodies which are around us.
The steam radiators are placed in this room for the express purpose
of sending out heat waves through the ether in this room. This is
the chief method of distributing heat, and it is hindered rather
than helped by the presence of the air. The walls, ceiling, floor,
furniture, people--everything here is sending out heat waves.

The fourth kinds of waves, which go out from the spark gap of our coil,
are also waves in the ether. They are still longer than heat or light.
We have ears for sound, eyes for light, and temperature sensation
for heat, but as yet we have not evolved a delicate sense organ for
detecting electric waves. At least few of us claim to have such a
sense. I will, however, undertake to make you feel electricity. I then
adjusted the coil so that each boy might take a mild electric shock
from it by touching the two knobs. That is by placing himself in the
spark gap. They agreed that although they could not hear, see, taste,
or smell electricity they were a little more familiar with it now,
having felt it.

Sound waves in air, as given out by the piano, vary in length from,
say, four inches to forty feet, those having the shorter wave length
being the higher pitched tones.

Light waves in the ether, as given out by the sun, vary in length
from, say, 1/60000 to 1/80000 of an inch, those having the shorter
wave length being the violet-coloured light, which may be seen in the
rainbow, and those having the longer wave length being the red-coloured
light of the rainbow or the sunset.

Heat waves, which are also waves in the ether, vary in length from
above 1/80000 to, say, 1/5000 of an inch. Roentgen or X waves are ether
waves, shorter than light; while Hertzian, or wireless telegraph waves
are very long ether waves, varying from a few feet to many rods in
length. Those used by Marconi in sending despatches across the Atlantic
Ocean are as long as 1000 feet, four or five of them cover a mile, and
12,000 of them cover the whole distance from Cape Cod to Poldhu.

Electric waves are easily broken up into the shorter heat waves, or the
still shorter light waves. On the other hand Roentgen waves are readily
transformed into the longer light waves, and are thus brought within
our powers of vision.

Sound waves of various lengths (of high and low pitch) all travel at
the same speed (one mile in five seconds), else how would the piccolo
and the bass horn of the distant band sound together. So ether waves of
various lengths (light, heat, electricity, etc.) all travel at the same
speed, _i. e._, 186,000 miles per second.

For detecting the electric waves which may be sent out from the spark
gap of our automobile spark coil I shall ask you to help me prepare
a special piece of apparatus. One boy may file this silver ten-cent
piece and another may file this nickel five-cent piece, each gathering
the filings upon a piece of paper. A third boy may select a piece of
glass tubing about one eighth of an inch in the inside diameter, and
with a three-cornered file cut off a short piece, about one and a half
inches long, and smooth the ends with a wet file. A fourth boy may
select a piece of stout copper wire nearly as large as the bore of the
glass tubing, and cut from it two pieces, each about two inches long.
Wind one end of each of these with thread to make them fit snugly in
the glass tubing.

[Illustration: Fig. 182 Coherer]

We thrust one of the wires into the tube, then mixed equal parts of the
silver and nickel filings and put as much of the mixture into the tube
as we could hold upon the tip of a penknife blade, and then thrust in
the other copper wire. (See Fig. 182.) The ends of the wire were about
one eighth of an inch apart and the gap was loosely filled with the
metal filings. This was connected by short pieces of copper wire, as
shown in Fig. 183, to a dry battery cell, _B_, and a sensitive ammeter.
When all connections were made the needle of the ammeter remained at
zero, showing that no electric current was passing, that is, the
battery cell was unable to send any electricity through the metal
filings.

This is the apparatus which is to help us detect electric waves when
they pass about us. Electricity has been called invisible light, that
is, invisible to our eyes, and this apparatus has been called an
"electric eye" because it will detect electric waves in the ether, just
as our eyes may detect light waves passing through the ether.

[Illustration: Fig. 183]

We placed the automobile spark coil upon the table near to the tube
containing the filings of silver and nickel, and as soon as we made a
spark pass between the knobs the ammeter needle moved half way across
the scale, indicating that the spark had somehow influenced the metal
filings in the tube so that now they permitted the battery cell to send
some electric current through them and through the ammeter. I asked one
of the boys to tap the tube slightly with a lead pencil so as to jar
the metal filings, and as soon as he did so the needle of the ammeter
went back to zero.

[Illustration: Fig. 184]

The spark coil sent electric waves out in every direction, and those
which hit the metal filings made them cohere together. In that
condition they allowed the dry cell to send through them enough current
to move the needle of the ammeter. Tapping the tube made the metal
filings break apart again, in which condition they do not allow the
current of the cell to pass in sufficient quantity to move the needle.
This tube is called a _coherer_, because the filings in it cohere
together. The apparatus then serves to indicate when electric waves
are passing. As yet, however, it would not respond when the spark coil
was more than one foot away. Our next step was to attach extra pieces
of wire, each ten or twelve feet long, at either end of the coherer,
as indicated in Fig. 184. One of these wires was stretched out upon
the floor while the other one was connected with the wire of a picture
hanging upon the wall.

We now found that the coherer would respond when the spark coil was
operated several feet away. The extra wires which we had attached to
the coherer are called antennæ, because they suggest the long "feelers"
or antennæ of some insects.

[Illustration: Fig. 185]

Our next step was to put antennæ upon the spark coil also, as shown
in Fig. 185. One of these wires was stretched out upon the floor,
while the other one was connected with the wire of a picture hanging
upon the wall on the opposite side of the room from where the coherer
was. We now found that the coherer would respond when the spark coil
was operated in the farthest part of the room. With the wires which
were lying upon the floor extending toward each other, but lacking
several feet of touching, the coherer responded when the spark coil
was operated in various other rooms of the house, although the doors
between were shut. When the floor wires were connected to the water
pipes the coherer would respond when the spark coil was operated in
a neighbouring house. We tried a similar experiment, substituting an
ordinary electric bell for the spark coil. The coherer or electric eye
detected that ether waves were sent forth from an electric bell every
time a spark was produced in the bell. For this purpose connections
were made, as shown in Fig. 186. One dry battery cell was used to ring
the bell. The floor wire _a_, or, as it is usually called, the ground
wire, was connected to the binding post 1, and the other antenna was
connected to the screw 3, and then supported aloft on a picture hung
upon the wall. With this transmitter we sent waves across the room
which were detected by the coherer.

[Illustration: Fig. 186]

We constructed a simple spark coil as follows: We bought a pound of
No. 24 single cotton covered copper wire, such as is used in the
electro-magnets of bells. It was, when we bought it, wound upon a
wooden spool. We filled the hole in the centre of this spool with wire
nails. One dry cell was connected with this (Fig. 187). When the wires
at _d_ were touched together, and then separated, a spark was produced
at that point. A ground wire was connected at _b_, and an antenna at
_c_, as before. Using this apparatus now as a transmitter of ether
waves, we found that the coherer detected them.

[Illustration: Fig. 187]

We next gave our attention to making changes in the receiving
apparatus, not to change the coherer, but to provide substitutes for
the ammeter. A sensitive _relay_ was procured, which is essentially
like a bell or buzzer except that it does not clatter. It will be
readily understood, by referring to the accompanying Fig. 188, that
_R_ is a coil of insulated wire around an iron core exactly like what
we see in the electric bell. (In practice there will be a pair instead
of one of them.) Such coils are called electro-magnets, because when
electricity flows in the wires they become magnets, and will attract
iron. _A_ is an iron spring, _B_ is a dry battery cell and _C_ is the
coherer. Whenever an ether wave passes the coherer permits the battery
cell to send a current around the magnet of the relay, and it attracts
the iron spring _a_, so that it hits against the metal post _d_ with
a click. Whenever we used this to respond to ether waves the click of
the relay suggested the telegraph sounder. How it served in wireless
telegraphy will appear in the following pages.

[Illustration: Fig. 188]




XXII

RINGING BELLS AND LIGHTING LAMPS BY ELECTRIC WAVES


[Illustration: Fig. 189]

Harold was to have a birthday party, to which many of his school
friends were invited. For this occasion he prepared, with my help,
to perform for the girls and boys some electrical experiments, and
particularly to give all who chose to try it an electric shock. For
this purpose he had them all join hands, and the electric charge was
sent through the whole line at once. One thing he did shocked his
mother more than anything else. He instituted a mock court, at which
one of the boys was tried, convicted and condemned to be executed by
electricity. The whole affair was enacted with no great solemnity, but
the electrical experiment was voted a great success by the executed
"criminal." The following group of experiments, however, seemed to give
the most satisfaction: On a table was placed the coherer connected to
the relay, and in another room was placed the spark coil for sending
ether waves. He had this operated by a confederate whom he chose for
the purpose. He then connected two wires to the relay, one at _d_ and
the other at _e_ (Fig. 189). These ran to a battery cell and a bell in
a far corner of the room. At a given signal (a cough) the confederate
made a spark at the spark coil in the other room; this sent ether
waves through the partition between the rooms; the ether waves caused
the coherer to pass electricity from the dry cell No. 1, to close the
relay spring _R_. This acted like a switch to close the second circuit
through the dry cell No. 2 and the bell, which rang out to the surprise
of all. It continued to ring until he tapped the coherer tube and broke
apart the filings. When this had been tried to the satisfaction of all,
the company was invited to another room. Here they found an electric
train with tracks, train sheds, stations, tunnels, bridges, switches,
signals, etc., arranged upon a centre table. The electric train was to
be started by ether waves. A wire from the railroad track was connected
with _e_ of the relay (See Fig. 190). A wire from _d_ of the relay was
connected to the third rail through a battery of sufficient strength
(Battery 2). The electric train completed the circuit by connecting
the tracks with the third rail. All heard the crack of the spark coil
in the adjoining room, and saw the train start immediately. Ether
waves had caused battery 1 to close the relay _R_. This had closed the
circuit so that battery 2 might run the train, of course by means of a
motor in the train. He tapped the coherer. The relay spring _R_ flew
open and the train stopped. Presently another crack from the adjoining
room, and the train instantly started again. When all the details of
the electric train had been examined the company was invited to go to
the dining room, which was dimly lighted by candles. All were seated
and busily conversing when the crackling noise of the spark coil was
again heard, and a group of little electric lights flashed forth upon a
birthday cake. The wires from the lamps and a battery to run them had
been connected with the binding posts _d_ and _e_ of the relay.

[Illustration: Fig. 190]

The chandelier over the dining-room table had a pendant push button
_A_ (Fig. 191), with which the regular electric lights could be turned
on and off. This I had removed and extended the wires down upon the
table. It was only necessary to connect these to the binding posts _d_
and _e_ of the relay, and the next wave from the spark coil lighted the
chandelier.

[Illustration: Fig. 191]

The flexible wires underneath the dining-room table with which the
maid is usually summoned from the kitchen were next extended up and
connected with _d_ and _e_ of the relay, and the maid was called in
by an ether wave. She brought with her a tray in the centre of which
stood an earthenware cup, such as is used for baking custard. This had
been filled with a mixture of granulated sugar and powdered potassium
chlorate. Four dry battery cells stood around this upon the tray
connected in series (Fig. 192). A very small iron wire connecting
two of these cells dipped into the sugar mixture. Two wires from the
battery were connected to _d_ and _e_ of the relay. At the proper
signal an ether wave was sent out by the spark coil. The coherer closed
the relay and the relay acted as a push button to close the circuit of
the four cells upon the tray. The fine wire dipping into the sugar and
potassium chlorate got red hot. This caused the mixture to flash up and
burn in most beautiful coloured flames. (Fig. 193).

[Illustration: Fig. 192]

[Illustration: Fig. 193]

On this occasion Harold's friends gave him, with due formalities,
the degree of E. E., which they said meant _electrical expert_, and
ever since that night he has been called "the expert." I inquired of
the young folks, as their party was breaking up, if they understood
Harold's explanations of all these things, and he replied that he at
any rate understood them better having attempted to explain them.




XXIII

TELEGRAPHING BY ELECTRIC WAVES


The next time Harold and I experimented we arranged something to save
us the trouble of tapping the coherer each time we used it. We employed
simply an electric bell, _B_ (Fig. 194), from which we removed the
gong. By reference to the figure the arrangement will be understood.
Each time ether waves cause the metal filings to cohere and the battery
_B^{1}_ closes the relay _R_, battery _B^{2}_ causes the hammer of
_B^{3}_ to tap against the coherer. This causes the current to cease to
flow from _B^{1}_ and the relay opens again by its own spring.

[Illustration: Fig. 194]

[Illustration: Fig. 195]

Our next addition was a telegraph sounder as shown in Fig. 195. _B^{1}_
is a single dry cell, _C_ is the coherer, _R_ is the relay, _B^{2}_ is
now a battery of three cells. Part of its current goes to _B^{3}_,
the tapper for the coherer, and part of its current goes to the
electro-magnet of the telegraph sounder _S_. Ordinarily a spring holds
the iron strip _d_ up against the metal stop _a_, but when the current
passes through the electro-magnet it pulls down this iron strip with
a click against the metal stop _e_. But while this is happening _C_
is being tapped by _B_, and is ready to respond to each wave. It was
only necessary now to have some code of signals in order to communicate
by telegrams. We learned the system of dots and dashes, or short and
long periods marked off by the sounder, which all telegraphers use
and which is known as the Morse alphabet, and very soon Harold and
I were telegraphing from one room to another messages of several
sentences at a time, the Morse alphabet being told off on the spark
coil and being received through the coherer and telegraph sounder.
It was not long before Harold and one of the neighbours' boys were
exchanging messages between their homes, each having a spark coil and
the necessary receiving apparatus, and having extended their antennæ to
the top of the buildings into what are called in the wireless language
_aerials_.

[Illustration: Photograph by Helen W. Cooke. Induction Coil of a
Wireless]

The fever for wireless telegraphy spread like wild-fire among the boys.
In a few months they had formed a "wireless club." They had each read
anywhere from ten to thirty books and articles upon the subject, and
had secured the latest improved apparatus. They made it a practice
to spend hours daily at their instruments picking up and keeping on
file messages which were sent to and from steamers leaving the harbour
for European ports. On one occasion they showed me from these files
scores of messages--fond, personal, and supposedly private farewells to
friends and communications between business partners which they would
never have made on land without first closing the office door. The
boys had acquired a mass of technical knowledge upon the subject which
far exceeded my comprehension. But their teachers in school complained
that they would learn nothing else, and some of the boys had already
received warning that they might fail of promotion.

How to have compelling interests without riding hobbies is the great
problem for both boys and men. I have known many boys who could, or at
least would, do nothing well in school or out, except some specialty
like manual training or science. In later years they were so deficient
in education that they could hold no worthy position in anything. My
anxiety was to save my boy from such a fate. I was determined that he
should have a fair share of all kinds of culture. To this end we read
together much of biography, history and classical literature, ancient
and modern, through the medium of the English language.

As both prevention and cure of the wireless telegraph mania I deemed
it not necessary to suppress enthusiasm, nor to introduce obviously
useless tasks for the sake of the training which might be in them.
My method was, on the contrary, to encourage my boy to have several
hobbies which he might ride with enthusiasm, but to make it a rigorous
rule to exchange his "mount" occasionally.




XXIV

HALLEY'S COMET AND ELECTRICAL WAVES


[Illustration: Fig. 196]

It was the year 1910 and Halley's comet was approaching the sun. On
May 18 its tail might be expected to reach the earth. Astronomers had
requested all who might be possessed of wireless telegraph apparatus
to watch on that day for any peculiar behaviour of their apparatus so
that evidence might be obtained whether or not the comet sends forth
such ether waves as we call electricity. Harold desired me to explain
the whole matter to his group of friends, which I did on a subsequent
evening, as follows:

"Although Halley's comet has come within the earth's orbit about three
thousand times since its first recorded appearance, I know of no man
living who can give a satisfactory account of having seen it. Any one
who has seen it before must be at least seventy-five years old, for
it requires seventy-five years to make one complete circuit of its
own orbit. But no one who is now seventy-five could have observed it
intelligently, and even one who is now eighty-five years old would
have to tell what he saw when he was ten years old and has remembered
for seventy-five years. Furthermore, any account of how it looked on a
former return is no guide to how it may appear on this trip. You may
properly think of the comet as a group of solid pieces no bigger than
the stones you may throw, scattered, two or three to the mile, through
a space 12,500 miles broad. This extremely thin cloud of particles does
not reflect enough sunlight to be visible, even in a telescope, in
any part of its journey, and hence we should be wholly unaware of its
existence if it did not sometimes have the strange faculty of giving
out light of its own _while in that part of its own orbit nearest to
the sun_. At such a time there is a hazy light enveloping the mass of
small bodies, and streaming away sometimes many million miles from
them. The mass of small bodies is generally referred to as the nucleus,
and the stream of luminous gas which the nucleus gives forth is called
the tail, though it reminds me more of a search-light.

"It does not trail along behind the comet but always points away from
the sun (Fig. 197). The normal thing for a comet to do is to begin to
develop a faint light and a short streamer as it gets near to the sun,
to have its light grow brighter and its streamer to grow longer until
it reaches the point nearest the sun, and then to have its light grow
dimmer and the streamer grow shorter as it recedes from the sun.

[Illustration: Fig. 197]

"It has many times been suggested that this strange search-light
appearance may be an electrical phenomenon, some form of ether waves
which the comet sends forth when under the immediate influence of the
sun. But not all comets are alike in this matter, nor does the same
comet always act alike on succeeding trips, so that we may not predict
what Halley's comet will do on this visit. It would be natural to
suppose that Halley's comet, like radium, might in time lose the power
to radiate off material, in which case it might at length become wholly
invisible to us, even though it continued to travel in its wonted
path. Our only way of knowing of its existence then would be that on
its returns some of its small pieces might be attracted to the earth
and enter our atmosphere as meteors. This sort of thing is continually
happening, and may be the last reminders of once brilliant comets.

"For almost a century it has been the common belief that light is
merely a wave motion in the ether. Our eyes respond to ether waves of
certain length only. Waves a little longer than those which affect
our eyes are felt by us as heat waves. Waves still longer than those
of heat are the so-called electric waves. These we use in wireless
telegraphy. There are still shorter waves than those of light. These
affect the sensitive plate in photography. They help to form the green
material in the leaves of plants and the brilliant colours in flowers.
They assist in the fading of our clothes and the tanning of our skin.
These are called chemical waves. Still shorter waves in the ether than
those of which we have just spoken are the X rays, and all the strange
things which they may do have not yet been determined. Certain it is
that they can make dreadful sores in our flesh. They can penetrate
through wood and paper, but not metals. They pass readily through
flesh, but not bones. All such ether waves are treated in a book by
Sylvanus P. Thompson, entitled 'Light Visible and Invisible,' in which
he points out that electricity, heat, light, chemical rays, etc., are
all alike in being ether waves, and this was suspected by James Clerk
Maxwell and others half a century ago, and has come now to be quite
generally believed.

"Halley's comet, already having been _seen_ upon this return, must
be sending out those ether waves which we call light; whether it is
also sending forth some of the other kinds of ether waves may yet be
determined."

My audience being chiefly composed of those persons who were present
at Harold's birthday party, they pressed me to tell them more about
wireless telegraphy and similar matters, and so I agreed to give them
at some future date some account of the history of these ideas. But my
present purpose was to start an interest in astronomy as an antidote
for the wireless epidemic, and so I invited all who desired to do so to
come again one week from that evening, bringing with them such opera
and field glasses as they might be able to secure. I promised to
show them how to make a telescope such as Galileo had more than three
hundred years ago. I agreed to go out with them several evenings and
scan the sky with our telescopes, and to tell them of some readable
books and articles upon astronomical matters.




XXV

HOW THE IDEA OF A UNIVERSAL ETHER DEVELOPED


The evening for the meeting of the Science Club had arrived. Its
membership had increased tenfold within a year. At its monthly
meetings, which were open to the public, an audience of two hundred,
old and young, was usually present--a number about three times that of
the regular membership. General science was now the study of this club.
At its weekly meetings, which only members attended, the studies of
specific topics by individuals, oftentimes illustrated by experiments,
were reported. These meetings were held in one of my laboratories,
while the open monthly meeting was always held in my lecture room, with
some rather famous speakers to instruct the audience. An enthusiastic
friend of science had given a fund with the stipulation that we should
engage the services of those who both knew their subjects and had
acquired the art of presentation. The fund was $10,000 and it yielded
$500 a year. I think beyond question it was doing more for science
than any other fund of ten times that amount which can be mentioned.

On the particular evening of which I am about to speak, the lecturer
told the members of the Science Club frankly how, beginning at the
age of thirteen, he had spent forty years of _enjoyment in study_,
that he had always found great satisfaction in the study of ancient
civilizations and literatures. He had been fortunate, he said, in
having teachers early in life who could make these subjects full of
meaning to him. His greatest satisfaction, however, during the last
twenty-five years had been found in tracing the development of modern
science, both in the evolution of its theories and in its applications
to modern industries. He said he was sure that young people of
high-school age would find it profitable to learn, for instance, how
the modern theory of combustion had developed slowly through the
centuries, even if to do so they must curtail somewhat their study
of how Greece and Rome developed and declined. He said that science
furnished a tremendously rich field of study for young people, which
as yet had been untouched by our schools, first, because educational
conservatism had made it impossible to determine the relative
importance of subjects of study, and, second, because education in
science had, for a brief period, found its worst enemies within its
own camp. He would like especially to commend on this evening some
historical studies in science, and had chosen for his subject, "How the
Idea of a Universal Ether Developed."

Men seem to talk freely now about the transmission of light, heat, and
electricity by means of the _ether_. How did this idea arise? Is it a
product of wild imagination? or did the idea develop out of experiences
which, if given to any person of fair intelligence, would yield the
same result?

A little over thirty years ago, at the Royal Institution of Great
Britain, James Clerk Maxwell (1831-1879) delivered a lecture on "Action
at a Distance." It was no new subject, but rather one of the oldest and
most often discussed subjects from the days of the ancient Greeks down
to the present. We talk of gravitation as an attraction or pull between
the various bodies of the universe, but how can they pull one another
without some material bond between? This was Sir Isaac Newton's great
puzzle which he never solved, though he expended upon it the greatest
efforts of his great intellect.

The sun appears to repel the tail of the comet, yet how can there be a
push without intervening material with which to push? When we speak of
light pouring or streaming in, do we think of it as a substance? When
we speak of warm bodies losing heat, or when we cover them to keep the
heat in, are we thinking of heat as a substance? What are heat, light,
electricity, magnetism, and gravitation?

These are no new questions. They are certainly older than history.
Various ideas have prevailed at different times. It is much easier to
change our ideas than to change our language. You occasionally see and
hear the words calorie and caloric used in connection with heat. They
stand for an idea, abandoned for three generations, that heat is a
substance called caloric, which saturates warm bodies and drains out
of them when they cool off. I hardly think these ideas either arise
or fall without good and sufficient reason. Each theory has been the
natural conclusion from our observations of nature as far as we have
gone with them. To be sure, it is difficult for us to see how men
acquired, from any observations of nature, the idea of light which
seems to have prevailed previous to the time of Aristotle, three and
a half centuries B.C. This idea was that objects were made visible by
something projected from the eye itself. Still, the questions which I
have indicated regarding heat, light, and electricity have impelled
men for many centuries to observe nature for hints as to the answers.
The doctrine of the universal ether as a medium for transmitting wave
motions, and of light, heat, and electricity as being motions of
different wave length, is the natural conclusion of the present time.
It may give place to another theory when we have further facts to
reason upon. Imagine your never having seen a harp or other musical
instrument. Would it require a long time, do you think, for you to
find out its use, at least to this extent, that it will produce tones
whenever the strings are made to vibrate? That the short strings
vibrate more rapidly than the long ones, and at the same time produce
tones of a higher pitch? Imagine that having become familiar with
the harp you should successively come upon scores of other musical
instruments of very differing types. You would soon become adept at
divining their uses. Now, a study of the microscopic structure of the
eye, for one thing, would suggest that light may be in the nature of a
vibration. Scores of other lines of study in a similar manner have at
length brought all who pursue them to the conclusion that light is a
form of vibration.

Robert Hooke in England (1631-1703) and Christian Huygens in Holland
(1629-1695), back in the seventeenth century seem to have been the
first to give expression to this idea, which was nothing more than
an inkling in Hooke's mind, but which was the necessary result of
observations on the part of Huygens. For nearly a century the idea lay
dormant, largely because Sir Isaac Newton (1642-1727), the cleverest
thinker of his time, opposed it. It was perhaps unfortunate for the
success of the theory that Huygens, its founder, adopted the word
ether, for that was an old term, and had been very badly overworked.
The word ether, or æther as it was often written, had been invented
in the days of ignorance, for such foolish reasons as: (a) because
"nature abhors a vacuum," or (b) "for planets to swim in," or (c) "to
constitute electric atmospheres and magnetic effluvia," or (d) "to
convey sensations from one part of our bodies to another."

"When we remember," says Maxwell, "the mischievous influence on science
which hypotheses about æthers used formerly to exercise, we can
appreciate the horror of æthers which sober-minded men had during the
eighteenth century."

Newton in England (1642-1727) and Laplace in France (1749-1827) stoutly
opposed the undulatory theory of Huygens and championed a corpuscular
or emission theory, that light-giving and heat-giving bodies emit a
subtile fluid.

There is no other instance in the whole history of modern physics in
which truth was so long kept down by authority. Fresnel (1788-1827)
and Arago (1786-1853) in France appear to be the only persons during
the eighteenth century who caught a clear vision of the truth of the
undulatory theory.

But it remained for Mr. Thomas Young (1773-1829), a colleague of Sir
Humphrey Davy at the Royal Institution, in his Bakerian lecture (1801)
on "Theory of Light and Colour" to bring together such good evidence
for the ether wave theory that it has hardly been questioned since.

Young, like Davy, was a most remarkable man in literature and in
science. It was he who first deciphered the Rosetta Stone, now in
the British Museum, and gave us a key to the Egyptian hieroglyphics.
Probably he was the only man who was able to overthrow the influence of
Newton's authority even a century after Newton did his work.

Faraday's (1791-1867) chief work as director of the laboratory of the
Royal Institution, London, was a study of ether phenomena, particularly
electric and magnetic. About seventy-five years ago he became
impressed with the fact that although wires may give direction to an
electric current the electric influence is not confined to the wires,
but may permeate more or less widely the region about them.

Nearly fifty years ago Maxwell (1831-1878) professor of physics at
Cambridge University, England, conceived the idea that light is
electricity of a very short wave length.

Nearly twenty-five years ago Heinrich Hertz (1857-1894), in Germany,
proved by experiments the existence of electric waves, and measured
their length and velocity, determining their various characteristics as
compared with light.

About fifteen years ago Marconi developed a wireless telegraph
apparatus, which made it possible to use electric waves for purposes of
communication.

Thirteen years ago (1897) the first wireless telegraph company was
formed. Eleven years ago (1899) the international yacht races in
New York Harbour were reported by wireless telegraph, and bulletin
boards in New York City announced to waiting crowds the details of the
race while it was in progress. Nearly ten years ago (1901) wireless
despatches were first sent across the Atlantic Ocean. Wireless
telegraphy was opened for public use in 1905, and very soon the company
began to coöperate with the regular telegraph companies. Nearly all
coastwise and trans-Atlantic steamers are now equipped with wireless
telegraph outfits, and a law has passed both houses of Congress
making it obligatory on the part of steamers which carry fifty or
more passengers to have such equipment. On several disabled steamers,
notably the _Republic_, loss of life has been averted by the wireless
emergency call for help, to which the captains of all steamers feel
obliged to respond. If you desire to communicate with a friend who
left for Europe several days ago, you simply write him a telegram,
addressing it to his ship, and deliver it at your nearest telegraph
office. Each telegraph office has a record of the location of every
ship having a wireless telegraph outfit. It despatches your message to
the wireless station along the coast which is nearest to your friend's
steamer, and from this station it is sent on the ether to the ship.
Or in some cases it may be repeated from one ship to another along
the Atlantic highway until it reaches the desired one. Thus also news
of important events on either continent is distributed daily on board
ships which are crossing the ocean. There are said to be more than
50,000 amateur wireless stations in the United States, and already
Congress is taking steps to regulate the use of the wireless telegraph
in order to prevent interference with Government and other important
messages.

More than three dozen books and countless magazine articles have
already been written upon wireless or ether wave telegraphy. Hundreds
have and thousands are contributing to our knowledge of ether wave
phenomena. If the names of all who have said or done something to
render stable the foundations of this idea of a universal ether, whose
undulations account for the phenomena of heat, light, and electricity,
were to be mentioned, the list would contain nearly all the important
workers in the field of physics for the last century.




XXVI

ELECTRIC CURRENTS CANNOT BE CONFINED TO WIRES


Harold said that if electricity was so much like light that it could
go without wires he thought light ought to be enough like electricity
to be conducted by wires on occasions. I told him that I had no hope
of being able to confine light to a wire; indeed, if the Science
Club would give me an opportunity I would show them that even when
electricity follows the general direction of a wire its influence
is not confined to the wire. As a result of this bid I received an
invitation to address an open meeting of the Science Club.

[Illustration: Fig. 198]

In my first experiment on that occasion I took a one-pound spool of
No. 24 cotton-covered copper wire and crowded the hole in the spool
full of wire nails _A_ (Fig. 198). I disconnected the wires from an
electric drop lamp and connected them to _b_ and _c_, the ends of the
wire from the spool. Our electric lighting circuit was what is called
the _alternating current_. I also had a second spool, _B_, precisely
like the first. The wires from this were connected to a miniature lamp,
_L_, such as is used at the switchboard of a telephone exchange. We
then screwed the drop-light plug into the chandelier and turned on the
electric current. I brought spool _B_ with the miniature lamp near to
spool _A_, as shown in Fig. 199, and when it was within a distance
of about two inches the little lamp lighted up to full brilliancy,
thus showing that while the electric current is passing in the wire
of spool _A_ its influence is not confined to the wire, but exhibits
itself in the region outside of the wire. To illustrate still further
this fact we substituted an electric bell in the place of the lamp
_L_, and when the spool _B_ was brought near to _A_ the bell rang. But
the most striking illustration was obtained when a telephone receiver
was put in the place of _L_. With this held to the ear while the spool
_B_ was brought toward _A_ a humming sound could be heard when _B_ was
about a foot distant from _A_. This sound grew rapidly louder as _B_
approached _A_, until, when the spool _B_ rested upon the spool _A_, a
sound like the peal of a pipe organ was heard all over the apartment.
The tone was very nearly that of the key on the piano which is two
octaves below middle _C_. I unscrewed the cap on the large end of the
telephone receiver, took it off, and moved the thin iron diaphragm to
one side, when it began to dance about at great speed. It was keeping
time with the dynamo, five miles away, which generated the electric
current. The dynamo changed the direction of the electric current sixty
times per second, and this made sixty vibrations per second. The dynamo
sent out ether waves which affected the telephone receiver, although
the receiver was not connected to the dynamo by wires.

To emphasize the fact that the dynamo had lighted the lamp, rung the
bell and made the telephone receiver hum without being connected with
them, I repeated all these experiments in a different way. Spool _A_,
connected as before with the electric lighting circuit, was concealed
beneath the table. For spool _B_ I substituted spool _C_ (Fig. 199), on
which the wire was wound so as to appear like a candlestick. On the top
of this was placed the miniature electric lamp screwed into a miniature
socket and connected to the wires of the spool. This "Witches'
Candle," as we called it, was sitting unlighted upon the table when I
called attention to the fact that if I moved it to a certain spot upon
the table it flashed into full light. (Of course this spot was directly
over spool _A_.) I moved it slowly away from that spot and its light
slowly grew dim and disappeared.

[Illustration: Fig. 199]

On the table was also sitting a cream pitcher in which I had placed
spool _B_ with a buzzer attached to it. Remarking that this pitcher
groaned for more cream whenever it was empty, and thus of its own
accord called the waiter, I moved it to the spot on the table directly
over spool _A_, when the buzzer gave forth a sound like a husky
bumble-bee shut up in a resounding bottle. At this signal my assistant
came in and took up the pitcher and placed my silk hat upon the table,
when it instantly boomed forth a base note two octaves below middle _C_
of the piano. Out of the hat I took a coil and the telephone receiver
and the mystery was solved.

[Illustration: Fig. 200]

In 1819 Hans Christian Oersted in Denmark (1777-1851) first noted
that the region about a wire carrying an electric current has an
influence upon a magnet. I will show this fact by a simple experiment.
I magnetize a stout sewing needle by drawing it from end to end across
the pole of a steel magnet, and by means of a triangular piece of paper
and a fine thread I suspend it a few inches above the table (Fig. 200).
I then lay upon the table a piece of wire parallel with the needle and
fasten one end of it to one binding post of a dry cell. Whenever I
touch the other end of the wire to the other binding post of the cell,
thus sending an electric current through the wire, the magnetized
needle is deflected at right angles.

This experiment, performed by Oersted, seems to have started Faraday
upon that wonderful series of researches which has resulted in giving
us the dynamo.




XXVII

WIRELESS TELEGRAPHY IN EARNEST


We had decided to let Harold make a trip to Europe alone. The first
message from him after his departure was a brief note to his mother
saying that they had had a turbulent voyage, but all had landed safely
upon the other side, none the worse for their experiences.

The next day a number of letters came to me from total strangers. One
of these ran as follows:

My Dear Sir:

Prompted by my own impulses, and urged to do so by the passengers under
my charge, I improve this first opportunity to express to you our high
appreciation for your noble but very modest son, to whom more than to
any one else we owe the lives of all on board our fated ship.

I am sending this direct to you both, because I understand a father's
heart and because the young man escaped as soon as we came to land,
without any of us learning his address. I beg you will communicate
to him the desire of the president of our company to meet him and
personally to thank him for his gallant conduct. I am also instructed
to say that whenever Harold desires to cross the ocean the best which
any ship I may command can afford will be his without charge.

                               Very respectfully yours,
                                        -------- Captain.
                                                S. S.

Another letter was the following:

My Dear Sir:

Permit me to congratulate you on having such a heroic and
self-possessed son. We, his fellow passengers, are, if possible, as
proud of him as you must be.

I fear that his account of the affair will not do himself full justice,
and so, with your permission, I will give you the full details as I
have gathered them from the passengers, from the crew, and from my own
observation.

During the last night of our voyage a thick fog closed about us. The
constant blowing of the fog whistle made the night dismal. Few persons
slept at all. About two o'clock in the morning the ship struck a reef,
and instantly it seemed as though every person on that ship reached the
decks at the same time. The water poured in and put out the fires. The
ship heeled badly, and it seemed that any minute she might slip off
the reef on which she was resting into deep water and go down. To add
to our horror fire broke out. It seems to have started in the wireless
operator's room.

Very much damage was done to the wireless outfit itself, and the
operator was badly burned, so much so that he was taken to the ship's
hospital suffering with many painful and dangerous wounds.

Meanwhile the flames spread rapidly and we were unable to summon help.
The crew and many of the passengers fought the flames, but with little
success.

In the midst of our despair word passed around the ship that an unknown
boy from among the passengers was sending the C. Q. D. message to
all the world by wireless. It was afterward learned that your Harold
was the youth. He had repaired the damaged apparatus sufficiently to
establish connection with a storage battery which he found, and, under
the captain's direction, was sending forth that hurry call for help
known to all the wireless fraternity and heeded by all sea-faring men.
I learned that your boy was not a regular operator, but that somehow
he had learned to send this message and also to send out the captain's
calculations of our position at sea. He was also able to detect that
his call had been heard and that help was coming, although he could not
understand much that came to his instrument in reply to his calls. I
learned, also, that he was one of the first to reach the operator's
room and to give assistance. He was himself badly burned, so much so
that one hand was being dressed by a nurse while he was continually
using the other to operate his instrument.

I can testify, my dear sir, that he appeared to be the calmest and most
self-possessed person on board that ship, as I saw him in the glare of
the dreadful flames which lit up the blackest night.

I am an artist and would like to attempt to paint that scene, which has
left its lasting impression upon my soul. I beg that you will allow
me to exhibit it for a time in several of our galleries and finally
present it to your family.

Help came none too soon. We were all transferred to other boats, but
the sea was rising, and scarcely had we reached a safe distance when
the burning ship slipped into the sea and disappeared.

I do not know by which boat your son reached the land. In the great
confusion I lost sight of him at last. He has doubtless communicated
with you by this time, and I shall esteem it a great favour if you will
put me in communication with him again.

In order that I may do justice to him in the painting I would like to
arrange with him a few sittings while he is in Europe.

Could you kindly send me a photograph of him which will assist me
somewhat?

                             Most sincerely and gratefully yours,
                                                        --------.

The letter contained several references to mutual acquaintances.

       *       *       *       *       *

Harold's letters have been frequent and full of the pleasure he is
having in European travel, but the only thing he has said about the
voyage is that "it was not worth so much fuss."

[Illustration]

THE COUNTRY LIFE PRESS
GARDEN CITY, N. Y.

       *       *       *       *       *


Transcriber's Notes:

Obvious typos and inconsistencies in spelling have been corrected:
  p31. intrument -> instrument
  p35. mantain -> maintain
  p48. represents the [the] counter-electro-motive force
  p64. 2 volts × .1 ampere = .6 watts. ->
       6 volts × .1 ampere = .6 watts.
       The correct voltage is deduced from the preceding paragraph.
  p141. 55 ampere -> .55 ampere
  p168. familar -> familiar
  p173. preceptible -> perceptible
  p229. - p230. countershaft -> counter shaft
  p259. H_{2}SO^{4} -> H_{2}SO_{4}
  p295. Note C refers to C´ not C´´
        and these should be labelled C, and C,,
        to denote octaves below middle C.
  p316. electri-tricity -> electricity
  p356. oufit -> outfit

Throughout the text:
  The few cases of "volt-meter" have been changed to "volt meter"
    which has been used for the majority of the text.

  The single instances of watt meter and watt-meter have been changed
    to wattmeter which has been used for the majority of the text.

  The few cases of  "electro magnet" have been changed to
    "electro-magnet" which has been used for the majority of the text.

In the Table of Contents:
  Chapter XII page number changed from 118 to 218
  Chapter XV  name changed from "Electricity from Chemical Action and
       Chemical Action from Electricity" to match
       text which reads "ELECTRIC CURRENTS FROM CHEMICAL ACTION AND
       CHEMICAL ACTION FROM ELECTRIC CURRENTS"

In the Table of Illustrations:
  "Operating a Switchboard" changed to match caption which reads
  "Operating the Switchboard"

p63. The example of Morse code given is correct for "Original" or
American Morse. It has some differences from Continental or
International Code which is the current standard. The spacing of the
dots is significant.